FORM SIX: PHYSICS STUDY NOTES-TOPIC 5: ENVIRONMENTAL PHYSICS

(i) Agriculture physics

– Influence of solar radiation on plant growth.

– Influence of wind, humidity, rainfall and air temperature on plant growth.

– Soil environmental component which influence plant growth.

(ii) Energy from the environment

Photovoltaic energy

Wind energy

Geothermal energy

Wave energy

(iii) Geophysics (Earth quakes)

Elastic rebound theory

Types of seismic waves

Propagation of seismic waves

Seismology

(iv) Environmental pollution

Types of pollutant in the atmosphere

Transport mechanisms of atmospheric pollutant

Nuclear waste and their disposal

Effects of pollution on visibility and optical properties of materials.

INTRODUCTION

Environmental physics is an interdisciplinary subject that integrates the physics processes in the following disciplines: the atmosphere, the biosphere, the hydrosphere, and the geosphere.

Environmental physics can be defined as the response of living organisms to their environment within the framework of the physics of environmental processes and issues.

It is structures within the relationship between the atmosphere, the oceans (hydrosphere), land (lithosphere), soils and vegetation (biosphere).

It embraces the following themes:

(i) Human environment and survival physics,

(ii) Built environment

(iii) Renewable energy

(iv) Remote sensing

(v) Weather, climate and climate change, and

(vi) Environmental health.

The environment may be defined as the medium in which any entity finds itself, For example, for a cloud its environment may be the region of the atmosphere in which it is formed.

AGRICULTURE PHYSICS

Agriculture physics is concerned with physics environment in relation to plant growth.

(a) Influence of Radiation Environment on Plant Growth

Radiation environments. Refer to radiations present in the atmosphere, commonly coming from the sun.

Components of solar radiation

The main components of solar radiation are:

(i) Visible light

(ii) Infrared radiation, and

(iii) Ultraviolet radiation.

HEATING EFFECT OF SOLAR RADIATION ON PLANTS

Positive effect

An optimum amount of heat on plant favours the process of photosynthesis. This enables a plant to make its own food and hence provide its growth.

Negative effects

(i) Excessive solar radiation (ultraviolet light) on plants leads to bleaching of green pigment (chlorophyll). This lowers the amount of food produced by photosynthesis to plant and hence a plant may die.

(ii) Excessive solar radiation on plants leads to excessive water loss in the form of water vapour commonly on plant leaves (transpiration). Hence wilting (drying) of plants may occur.

(b) Influence of Aerial Environment on Plant Growth

Aerial environments refer to the atmospheric condition resulting from a series of processes occurring in the atmosphere. These include air temperature, wind, humidity and rainfall.

WIND EFFECT ON PLANT GROWTH

Positive effects

(a) Wind acts as pollinating agent for some plants and hence favours plant productivity.

(b) Wind also favours evaporation of water from plant leaves and thus maintains water balance for proper plant growth.

Negative effects

(a) Excessive wind on environments leads to plant breaking or cutting of tree branches. This may lead to the death of plant.

(b) As the wind speed increases further, cell and Cuticular damage occurs, followed by death of plant tissue, and a gnarled appearance becomes more apparent.

(c) At low wind speeds, the effect seems to be an increase in transpiration, which results in water stress. This stress causes the plant to adapt by decreasing leaf area and internodes length, while increasing root growth and stem diameter.

(d) Strong wind may also cause shade off flowers; this lowers plant productivity.

Effect of Rainfall on Plant Growth

Positive effect

An optimum amount of rainfall on plants favours its growth. Water is a raw material for the process of photosynthesis from which plants obtain their food and hence their growth.

Negative effect

Excessive rainfall leads to water logging in soil which in turn leads to root spoil and hence the death of plant.

Effect of Humidity on Plant Growth

Positive effect

Favourable humidity on plants help plants to conserve water for various activities and in seeds helps the development of new leaves.

Negative effect

Low humidity results into a greater rate of transpiration and hence may result into plant drying.

Effect of Air Temperature of Plant Growth

Positive effect

An Optimum temperature on plants enhances enzymic activities which in turn gives favourable conditions for plant growth.

Negative effect

(a) High temperature denature enzymes commonly for photosynthesis and hence the death of plant.

(b) Low temperature inactivates the plant growth enzymes, hence low growth rate.

Wind Belts

Wind belts are seasonal strong wind moving in a specified direction in a certain region of the earth.

The global wind belts are formed by two main factors:

(i) The unequal heating of the earth by sunlight and

(ii) The earth’s spin.

Here is a simple explanation of the process

The unequal heating makes the tropical regions warmer than the Polar Regions. As a result, there is generally higher pressure at the poles and lower at the equator. So the atmosphere tries to send the cold air toward the equator at the surface and send warm air northward toward the pole at higher levels.

Unfortunately, the spin of the earth prevents this from being a direct route, and the flow in the atmosphere breaks into three zones between the equator and each pole.

These form the six global wind belts: 3 in the Northern Hemisphere (NH) and 3 in the Southern (SH). They are generally known as:

(1) The Trade winds, which blow from the northeast (NH) and southeast (SH), are, found in the sub tropic regions from about 30 degrees latitude to the equator.

(2) The Prevailing Westerlies (SW in NH in SH) which blow in the middle latitudes.

(3) The Polar Easterlies which blow from the east in the Polar Regions.

Effects of wind belts to plant

1. Wind belts because the loss of plant leaves and flowers hence lower plant productivity and growth. Loss of leaves lowers the rate of photosynthesis.

2. Wind belts sometimes cause plants to lean in direction of moving wing. This changes their direction of growth

3. Trees are broken by the strong wind.

Soil is composed of both rock particles and organic matter (humus) – the remains of plants and animals in various stages of decomposition. The humus serves as food for many living organisms. Within the soil is a large population of animals, plants. These break down the humus into soluble substances that can be absorbed by the roots of large plants.

Components of a soil

Soil is composed of:

( (a) Air, 25% by volume which supports life of soil organisms,

(b) Water, 25% which dissolves minerals so that are easily absorbed by plants,

(d) Inorganic matter (minerals), 45% by volume,

(e) Biotic organisms, micro – organisms like earth worm, centipedes, millipede, bacteria which decompose organic matter.

Types of soil

(i) Sandy soil

(ii) Silt soil,

(iii) Clay soil, and

(iv) Loamy soil (sand + silt + clay soil mixture)

Water Movement in the soil

Two forces primarily affect water movement through soils, (a) gravity and (b) capillary action.

Capillary action refers to the attraction of water into soil pores – an attraction which makes water move in soil. Capillary action involves two types of attraction – adhesion and cohesion.

Adhesion is the attraction of water to solid surfaces.

Cohesion is the attraction of water to itself.

Speed of water in a particular soil type depends on:

(i) How much water is in the soil, and

(ii) Porosity of the soil.

The movement of water in the solid is mainly due to gravity. The porosity gives a measure of how much water the soil can hold and the rate at which water flows through the soil. Large pore spaces give a faster rate and vice versa.

An experiment to study water movement in soil

An experiment to demonstrate the rate of flow of water in the soil is done using a glass tube and sand type filled in it. Water is poured into the tube and the time taken for water to reach the bottom of the tube in notes.

i. Sand soil have large pore spaces thus allows water to travel downwards through it at a fastest rate.

ii. Clay soil can hold water as has very fine pore spaces.

iii. Loamy soil allows water movement at a medium rate.

Heat transfer in the soil

Within the soil heat is transferred by a conduction process. Since soil is poor conductor of heat most of the heat from the atmosphere appears at the surface of the earth.

An optimum soil temperature favours plants growth but a high temperature can lead to the rotting of plant roots.

(d) Techniques for the Improvement of the Plant Environment

Plant environment can be improved by using wind breaks, shading and mulching.

Shading

Shading is the process of obstructing plants from excessive solar radiation.

Positive Impacts of Shading

1. Prevents excessive loss of water by plants through transpiration. This enhances plant productivity.

2. Preserve moisture in the soil and hence water supply to plant.

Mulching

Mulching is the process of covering the soil by dry leaves, grasses and or papers.

Benefits (Advantages) of Mulching

1. Improve soil moisture. Bare soil is exposed to heat, wind and compaction loses water through evaporation and is less able to absorb irrigation or rainfall. Using mulches, the soil has greater water retention, reduced evaporation, and reduced weeds. Mulch can also protect trees and shrubs from drought stress and cold injury

2. Reduce soil erosion and compaction. Mulches protect soils from wind water, traffic induced erosion and compaction that directly contribute to root stress and poor plant health.

3. Maintenance of optimal soil temperatures. Mulches have shown to lower soil temperatures in summer months. Extreme temperatures can kill fine plant roots which can cause stress and root rot. Mulches protect soils from extreme temperatures, either cold or hot.

4. Increase soil nutrition. Mulches with relatively high nitrogen content often result in higher yields, but low nitrogen mulches, such as straw, sawdust and bark, can also increase soil fertility and plant nutrition.

5. Reduction of salt and pesticide contamination. In arid landscapes, evaporating water leaves behind salt crusts. Because mulches reduce evaporation, water is left in the soil and salts are diluted. Organic mulches can actively accelerate soil desalinization and help degrade pesticides and other contaminants.

6. Improve plant establishment and growth. Mulches are used to enhance the establishment of many woody and herbaceous species. Mulches improve seed germination and seed survival, enhance root establishment, transplant survival, and increase plant performance.

7. Reduction of disease. Mulches will reduce the splashing of rain or irrigation water, which can carry spores of disease organisms to stems and leaves of plants. Populations of beneficial microbes that reduce soil pathogens can be increased with mulches. Mulches can combat disease organisms directly as well.

8. Reduction of Weeds. Using mulches for weed control is highly effective. Mulches can reduce seed germination of many weed species and reduce light, which stresses existing weeds.

9. Reduce pesticide use. Mulches reduce weeds, plant stress, and susceptibility to pests and pathogens which translates to reduced use of herbicides, insecticides, and fungicides.

Mulch Problems (disadvantages of mulching)

1. i. Acidification. Some types of mulches can increase soil acidity.

2. ii. Disease. Many mulches made from diseased plant materials can be composted or treated at temperatures that kill pathogens that can be transmitted to healthy plants.

3. iii.Pests. Many organic mulches, especially wood – based mulches, have the reputation as being “pest magnets”.

4. iv. Weed contamination. Improperly treated crop residues and composts as well as bark mulches are often carriers of weed seed. Mulch must be deep enough to suppress weeds and promote healthy soils and plants. Weed control and enhanced plant performance are directly linked to mulch depth.

v. Wind Breaks

Wind breaks are long rooted strong plants (trees) that are used to obstruct the path of wind or to slow down the wind.

Windbreaks provide many benefits to soil, water, plants, animals and man. They are an important part of the modern day agricultural landscape. Windbreaks come in many different sizes and shapes to serve many different conservation purposes.

In agriculture, wind breaks protect small growing plants from strong blowing wind

Advantages of Windbreaks to Plant Environment

1. i. Control soil erosion. Windbreaks prevent wind erosion from causing loss of soil productivity. This eliminates plant roots stresses and thus favours plant growth condition.

2. ii. Increase plant yield. Windbreak research substantiates that field windbreaks improve crop yields which offsets the loss of production from the land taken out of cultivation.

3. Pesticide sprays. Windbreaks control pesticide spray drift and provide buffers to delineate property lines and protect neighbors.

EXAMPLES: SET A

Example 01

(a) What is agriculture physics? (02 marks)

(b) What are the components of a soil? How do they support the life of a plant? (06 marks)

Example 02

(a) What do you understand by the word environmental physics? (01 marks)

(b) Explain how the following climatic factors influence plant growth: air temperature, humidity, rainfall and wind. (06 marks)

Example 03

(a) What is mulching? (02 marks)

(b) Give two advantages and two disadvantages of mulching. (04 marks)

Example 04

(a) Explain two factors that primarily affect water movement in the soil (03 marks)

(b) Explain the soil environment that favours high crop yield (04 marks)

Example 05

(a) (i) Mention the components of solar radiation.
(ii) How do those components affect plant growth? (04½ marks)

(b) What are wind breaks? (02 marks)

ENERGY FROM THE ENVIRONMENT

ENERGY

Energy is defined as the capacity to do work Or is defined as ability to do work.

Energy is measured in Joules (symbol J)

Types of energy according to their usefulness

(i) High grade energy

(ii) Low grade energy

i. High grade energy is the energy that is easily transformed into other forms of energy and is more suitable for doing works.

Examples are chemical and electrical energy.

ii. Low grade energy is the one that is not easily transformed into anything else.

Examples are the kinetic energy of molecules due to their randomness and the potential energy due to the forces between molecules.

ENERGY SOURCES

There are two types of energy sources, namely:

(i) Primary energy sources,

(ii) Secondary energy sources.

i. Primary energy sources

Primary energy sources are sources of energy that are used in the form in which they occur naturally.

Primary energy sources fall into two groups:

(a) Finite energy sources,

(b) Renewable sources.

a. Finite energy sources are those energy sources that last after a number of years when exploited.

Examples are coal, oil, natural gas, and nuclear fuels.

b. Renewable energy sources: these cannot be exhausted. Examples are solar energy, biofuels, hydroelectric power, wind power, wave power, tidal and geothermal power, wind power, wave power, tidal and geothermal power.

ii. Secondary energy sources

Secondary energy sources are used in the non – natural form.

SOLAR ENERGY

Nature of solar energy

The sun’s energy is produced by thermonuclear fusion.

Not all of the solar radiation arriving at the edge of the Earth’s atmosphere reaches the Earth’s surface.

About 30% is reflected back into space by atmospheric dusts and by the polar ice caps.

About 47% is absorbed during the day by the land and sea and becomes internal energy (i.e. heats the Earth). At night this is radiated back into space as infrared.

23% causes evaporation from the oceans and sea to form water vapour. This results into rain and hence hydroelectric power.

-0.2% causes convection currents in the air, creating wind power which in turn causes wave power.

-0.02% is absorbed by plants during photosynthesis and is stored in them as chemical energy. Plants are sources of biofuels

Solar constant

Solar constant is defined as the solar energy falling per second on a square meter placed normal to the sun’s rays at the edge of the Earth’s atmosphere, when the Earth is at mean distance from the sun.

Its value is about 1.35 kWm2

The amount of solar radiation received at any point on the earth’s surface depends on:

(i) The geographical location,

(ii) The season, (summer or winter)

(iii) The time of the day, the lower the sun is in the sky the greater is the atmospheric absorption.

(iv) The altitude; the greater the height above sea level the less is the absorption by the atmosphere, clouds and pollution

PHOTOVOLTAIC DEVICES (SOLAR CELLS)

A solar cell (PV, cells) is a PN junction device which converts solar energy directly into electrical energy.

How it Works

PV cells are made of at least two layers of semiconductor material. One layer has a positive charge (p – type material), the other negative (n-type material). When light enters the cell, some of the photons from the light are absorbed by the semiconductor atoms, freeing electrons from the cell’s negative layer to flow through an external circuit and back into the positive layer. This flow of electrons produces electric current.

Uses of the solar cell

1. (i)Are used to power electronics in satellite and space vehicles.

2. (ii)Are used as power supply to some calculators.

3. (iii)Are used to generate electricity for home, office and industrial uses.

Series arrangement of solar cells

Solar panel (module) is a sealed, weatherproof package containing a number of interconnected solar cells so as to increase utility of a solar cell.

When two modules are wired together in series, their voltage is doubled while the current stays constant.

When two modules are wired in parallel, their current is doubled while the voltage stays constant.

To achieve the desired voltage and current, modules are wired in series and parallel into what is called a PV array.
The flexibility of the modular PV system allows designers to create solar power systems that can meet a wide variety of electrical needs, no matter how large or small.

Efficiency of a photovoltaic system

The output power of a solar cell depends on:

(i) The amount of light energy from the sun falling on a solar panel (the intensity of light).

(ii) The orientation of the solar panel. More electricity is produced if light falls perpendicular to panels.

(iii) The surface area of the panel. Large area collects more solar energy and hence greater electricity.

The best designed solar cell can generate 240 Wm-2 in bright sun light at an efficiency of about 24%.

Advantages of photovoltaic systems

1. Solar cells can produce electricity without noise or air pollution.

2. A photovoltaic system requires no fuels to purchase.

3. Panels of photovoltaic cells are used for small – scale electricity generation in remote areas where there is sufficient sun.

4. Net metering: This has the potential to help shave peak loads, which generally coincide with maximum PV power production.

5. The electricity from a PV system is controllable.

Disadvantages of photovoltaic systems

1. They require an inverter to convert the d.c output into a. c for transmission.

2. They produce electricity only when there is sunlight. Hence they need backup batteries to provide energy storage.

3. Suitable in areas which receives enough sunlight.

4. Photovoltaic large scale power generation is cost effective. This is due to large surface area of cells required for generating high power outputs and the need to convert d.c to a.c for transmission.

5. Compared to other energy sources, PV systems are an expensive way to generate electricity.

6. The available solar resource depends on two variables: The latitude at which the array is located and the average cloud cover.

WIND ENERGY

Winds are due to conventional currents in the air caused by uneven heating in the earth’s surface by the sun.

Wind energy is extracted by a device called wind turbine.

Wind speed increases with the height; it is greatest in hilly areas. It is also greater over the sea and coastal areas where there is less surface drag.

Wind turbines are also called aerogenerator or wind mills (old name)

Types of wind turbines

There are two types of wind turbines;

(i) Horizontal axis wind turbines (HAWT)

(ii) Vertical axis wind turbines (VAWT)

Horizontal axis wind turbine (HAWT)

HAWT has two or more long vertical blades rotating about a horizontal axis. Modern HAWTs usually feature rotors that resemble aircraft propellers, which operate on similar aerodynamic principles, i.e. the air flow over the airfoil shaped blades creates a lifting force that turns the rotor. The nacelle of a HAWT houses a gearbox and generator (alternator).

Advantage of HAWT

1. HAWTS can be placed on towers to take advantage of higher winds farther from the ground.

Disadvantages of HAWT

1. The alternator (generator) is paced at the top of the supporting tower.

2. Can produce power in a particular wind direction.

Vertical axis wind turbine (VAWT)

In vertical axis, the blades are long and vertical and can accept wind in any direction. The blades are propelled by the drag force on the blades as the wind flows.

Advantages of VAWT

1. It can harness wind from any direction

2. Typically operate closer to the ground, which has the advantage of allowing placement of heavy equipment, like the generator and gearbox, near ground level rather than in the nacelle.

Disadvantages of VAWT

1. Winds are lower near ground level, so for the same wind and capture area, less power will be produced compared to HAWT.

2. Time varying power output due to variation of power during a single rotation of the blade.

3. The need for guy wires to support the tower.

4. Darrieus VAWTS are not self starting like HAWTS. (More colorful picture and videos during lecture)

Power of a Wind Turbine

Consider a wind turbine with blades of length, r (area A), the wind speed is v and the air density is ρ. Assuming that the air speed is reduced to zero by the blades.

Kinetic energy of the wind, K.E =

Kinetic energy per unit volume

K.E per volume = ÷ volume =

The blades sweeps out an area A in one turn, so the volume of air passing in one second is Av.

Kinetic energy per second

= K.E per unit volume x volume per second

Extractable power

The power extracted by the rotating blades is much less than the available wind power. This is because:

(i) The velocity of the wind is not reduced to zero at the blades

(ii) Losses due to friction at the turbine and alternator

(iii) Due to losses in both the gear train and generator.

The power actually captured by the wind turbine rotor, PR, is some fraction of the available power, defined by the coefficient of performance, Cp, which is essentially a type of power conversion efficiency:

i. Cut in wind speed: This is the lowest speed at which the wind turbine will start generating power.

Typical cut – in wind speeds are 3 to 5 m/s.

ii. Nominal wind speed: This is the lowest speed at which the wind turbine reaches its nominal power output.

Above this speed, higher power outputs are possible, but the rotor is controlled to maintain a constant power to limit loads and stresses on the blades.

iii. Cut – out wind speed: This is the highest wind speed which the turbine will operate at.

Above this speed, the turbine is stopped to prevent damage to the blades.

Advantages of Wind Energy

1. Wind Energy is an inexhaustible source of energy and is virtually a limitless resource.

2. Energy is generated without polluting environment

3. This source of energy has tremendous potential to generate energy on large scale.

4. Like solar energy and hydropower, wind power taps a natural physical resource,

5. Windmill generators don’t emit any emissions that can lead to acid rain or greenhouse effect.

6. Wind Energy can be used directly as mechanical energy

7. In remote areas, wind turbines can be used as great resource to generate energy

8. In combination with Solar Energy they can be used to provide reliable as well as steady supply of electricity.

9. Land around wind turbines can be used for other uses, e.g. Farming.

Disadvantages of Wind Energy

1. Wind energy requires expensive storage during peak production time.

2. It is unreliable energy source as winds are uncertain and unpredictable.

3. There is visual and aesthetic impact on region

4. Requires large open areas for setting up wind farms.

5. Noise pollution problem is usually associated with wind mills.

6. Wind energy can be harnessed only in those areas where wind is strong enough and weather is windy for most parts of the year.

7. Usually places, where wind power set-up is situated, are away from the places where demand of electricity is there. Transmission from such places increases cost of electricity.

8. The average efficiency of wind turbine is very less as compared to fossil fuel power plants. We might require many wind turbines to produce similar impact.

9. It can be a threat to wildlife. Birds do get killed or injured when they fly into turbines.

10. Maintenance cost of wind turbines is high as they have mechanical parts which undergo wear and tear over the time.

NB: Even though there are advantages of wind energy, the limitations make it extremely difficult for it to be harnessed and prove to be a setback

GEOTHERMAL ENERGY

Geothermal energy is the energy from nuclear energy changes deep in the earth, which produces hot dry rock.

Geothermal energy originates from the heat retained within the Earth since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface.

Harnessing Geothermal Energy

Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth. In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application.

Geothermal energy is extracted by using two methods:

(i) A heat pump system

(ii) Hot dry rock conversion

The heat pump system

Hot aquifers are layers of permeable (porous) rock such as sandstone or limestone at a depth of 2 – 3 km which contains hot water at temperatures of 60 – 100C.

A shaft is drilled to aquifer and the hot water pumped up it to the surface where it is used for district space and water heating schemes or to generate electricity. A second shaft may be drilled to return the cool water to the rock.

The hot dry rock conversion

These are impermeable hot dry rocks found at depth of 5 – 6 km, have temperature of 200C or more.

Two shafts are drilled and terminate at different levels in the hot rock about 300 m apart. The rocks near the end are fractured by explosion or by methods to reduce the resistance
to the flow of cold water which is pumped under very high pressure (300 atm) down the injection shaft and emerges as steam from the top of the shallower shaft.

Unsaturated soil		Saturated soil
Soil type	Water speed	Soil type	Water speed
Sandy	Fastest	Sand	Slowest
Loamy	Moderate	Loamy	Moderate
Clay	Slowest	Clay	Highest

Uses of geothermal energy

Geothermal energy can be used for electricity production, for direct use purposes, and for home heating efficiency (through geothermal heat pumps).

Advantages of geothermal energy

1. Geothermal power plants provide steady and predictable base load power.

2. New geothermal power plants currently generate electricity at low cost.

3. Responsibly managed geothermal resources can deliver energy and provide power for decades.

4. Geothermal power plants are reliable, capable of operating about 98 percent of the time.

5. Power plants are small, require no fuel purchase and are compatible with agricultural land uses.

6. Geothermal plants produce a small amount of pollutant emissions compared to traditional fossil fuel power plants.

Disadvantages of geothermal energy

1. Many of the best potential resources are located in remote or rural areas, often of federal or state lands

2. Although costs have decreased in recent years, exploration and drilling for power production remain expensive

3. Using the best geothermal resources for electricity production may require an expansion or upgrade of the transmission system.

4. The productivity of geothermal wells may decline over time. As a result, it is crucial that

developers manage the geothermal resources efficiently.

WAVE ENERGY

Wave energy is the energy extracted from the ocean surface wave. Energy that comes from the waves in the ocean sounds like a boundless, harmless supply.

Machinery able to exploit wave power is generally known as a wave energy converter (WEC)

Wave power

Waves in the sea have kinetic energy and gravitational potential energy as the rise and fall.

Consider a sine wave of wave length λ spread over a width d the amplitude of the wave is a and the time period is T.

The power in a wave come from the change in potential energy of the water as it rotates on the circuit paths beneath the surface. It can be shown that the power carried forward by a wave is given by:

Wave Energy Flux

The mean transport rate of the wave energy through a vertical plane of unit width , parallel to a wave crest, is called wave energy flux.

arvesting wave energy

There are two type of system:

1. i. Offshore systems in deep water more than 141 feet deep. The Salter duck method.

(a) Pumps that use bobbing motion of waves.

(b) Hoses connected to floats on surface of waves. As float rises and falls , the hose stretches and relaxes, pressurizing the water which then rotates a turbine

2. ii. Onshore systems are built along shorelines and harvest energy from braking waves.

(a)Oscillating water columns are of concrete or steel and have an opening to the sea below the waterline. It uses the water to pressurize an air column that is drawn through the turbine as waves recede.

(b)A Tapchan is a tapered water system in sea cliffs that forces waves through narrow channels and the water that spills over the walls is fed through a turbine.

(c)A Pendulor device is a rectangular box with a hinged flap over one side that is open to the sea .Waves cause the flap to swing back and forth and this powers a hydraulic pump and generator.

Advantages of Wave energy

1. Renewable: It will never run out.

2. Environment friendly: Creating power from waves creates no harmful byproducts such as gas, waste, and pollution.

3. Abundant and widely available: Another benefit to using this energy is its nearest to places that can use it.

4. Variety of ways to harness: Current gathering method range from installed power plant with hydro turbine to seafaring vessels equipped with massive structures that are laid into the sea to gather the wave energy.

5. Easily predictable: The biggest advantage of wave power as against most of the other alternative energy source is that it is easily predictable and can be used to calculate the amount that it can produce.

6. Less dependency on foreign oil cost.

7. Non damage to land.

Disadvantages of wave energy

1. Suitable to certain locations: The biggest disadvantage to getting your energy from the wave is location. Only power plants and town near the ocean will benefit direct from it.

2. Effect on marine ecosystem: Large machine have to be put near and in the water gather energy from waves .These machines disturb the seafloor, changes the habitat of near-shore creatures (like crabs and starfish) and create noise that disturb the sea life around them.

3. Wavelength: Wave power is highly dependent on wavelength i.e. wave speed, wave length, and wavelength and water density.

4. Weak performance in Rough Weather: The performance of wave power drops significantly during rough weather.

5. Noise and Visual pollution: Wave energy generators may be unpleasant for some who live close to coastal regions. They look like large machines working in the middle of the ocean and destroy the beauty of the ocean. They also generate noise pollution but the noise is often covered by the noise of waves which is much more than that of wave generators.

6. Difficult to convert wave motion into electricity efficiently.

7. Difficult to design equipment that can withstand storm damage and saltwater corrosion.

8. Total cost of electricity is not competitive with other energy sources.

9. Pollution from hydraulic fluids and oils from electrical components.

TIDAL ENERGY
Tidal Power is the power of electricity generation achieved by capturing the energy contained in moving water mass due to tides.

Two types of tidal energy can be extracted: Kinetic energy of currents between ebbing and surging tides and potential energy from the difference in height between high and low tides.

Causes of Tides

Tides are caused by the gravitational pull of the moon, and to a lesser extent the sun, on the oceans. There is a high tide places near the moon and also opposite on the far side.

i. High (spring) tide: Occurs when there is full moon. The moon, sun and earth are in line the moon being between earth and sun. The pulls of the moon and sun reinforce to have extra high tides.

ii. Lowest (neap) tide: Occurs when there is half moon and the sun and moon pulls are at right angles to each other.

iii. Harnessing Tidal Energy

Tidal energy can be harnessed by building a barrage (barrier), containing water turbines and sluice gates, across the mouth of river. Large gates are opened during the incoming (flood) tide, allowing the water to pass until high tides, when they are closed.

On the outgoing tide, when a sufficient head of water has built up, small gates are opened, letting the potential energy of the trapped water drive the turbines and generate electricity.

Advantages of Tidal Energy

1. Decrease reliance on coal driven electricity so less CO2 emissions.

2. Changing technology allowing quicker construction of turbines, which in turn increases likelihood of investment with a shorter return.

3. Once constructed very little cost to run and maintain.

4. Tidal energy is renewable and sustainable.

Disadvantages of Tidal Energy

1. Intermittent energy production based around tides creates unreliable energy source.

2. High construction costs

3. Barrages can disrupt natural migratory routes for marine animals.

4. Barrages can disrupt normal boating pathways.

5. Turbines can kill up to 15% of fish in area, although technology has advanced to the point that the turbines are moving slow enough not to kill as many.

Tidal Power
If the tidal height (level) is h and the estuary area is A, then the mass of water trapped being the barrier is and the centre of gravity is h/2 above the low tide level.

The maximum energy per tide is therefore

Potential Energy of tide =

Averaged over a tidal period of T (approx. 12 hours a day), this gives a mean power available of.

Average tidal power =

Note that the efficiency of the turbines (generator) will determine how much of this tidal power will be harnessed.

EXAMPLES: SET B

Example 01

The power output p of a windmill can be expressed as where A is the area swept out by the windmill blades (sails),is the density of air, v is the wind speed and k is a dimensionless constant

(a) Show that the units on both sides of this expression are the same

(b) Sketch a graph to show how the power increases with wind speed as v rises from zero to 15ms-1

Example 02

The radiation received from the sun at the earth’s surface in a certain country is about 600 Wm-2 averaged over 8 hours in the absence of cloud.

(a) What area of solar panel would be needed to replace a power station of 2.0 GW output, if the solar panels used could convert solar radiation to electrical energy at an efficiency of 20%

(b) What percentage is this area of the total of the country (which is about 3 x 1011m2)?

(c) If the total power station capacity is about 140 GW, what percentage of the surface of the country would be covered by solar panels if all the power stations were replaced?

Solution

(a) Output of a solar panel

(b) Percentage area to the country

Percentage area to the country

Example 03

(a) What are aerogenerators?

(b) Estimate the maximum power available from 10m2 of solar panels and calculate the volume of water per second which must pass through if the inlet and outlet temperatures are 20C and 70C. Assume the water carries away energy at the same rate as the maximum power available. The specific heat capacity of water is 4200 Jkg-1 and solar constant is 1.4 kWm-2.

Solution

(a) Aerogenerators are devices that convert the kinetic energy of wind into electrical energy. E.g. windmill.

(b) Maximum power available from solar panel

GEOPHYSICS

Geophysics is the branch of physics which deals with the study of seismic waves and the Earth’s magnetic and gravity fields and heat flow.

Because we cannot directly observe the Earth’s interior, geophysical methods allow us to investigate the interior of the Earth by making measurements at the surface. Without studying these things, we would know nothing of the Earth’s internal structure.

STRUCTURE OF THE EARTH

Major zones of the earth

The earth is divided into two major zones, namely;

(a) Outer zone, and

(b) Inner zone.

a) Outer zone: the earth’s outer zone consists of;

(i) The hydrosphere – water bodies,

(ii) The atmosphere – gaseous envelope

(iii) The biosphere – living organisms, plant and animals

b) Inner zone: the earth’s inner zone consists of;

(i) The crust – lithosphere

(ii) The mantle – mesosphere,

(iii) The core – barysphere

Atmosphere is the envelope of gases that surround the Earth (oxygen, nitrogen, carbon dioxide, etc)

Hydrosphere is the water bodies filling the depressions in the Earth. Examples are rivers, oceans, seas, oasis,

Lithosphere is the solid outer most part of the earth.

EARTH’S LAYERS

Layers defined by composition

Layers are defined by composition because of density sorting during an early period of partial melting, Earth’s interiors not homogeneous.

 Crust – the comparatively thin outer skin that ranges from 3 kilometers at the oceanic ridges to 70 kilometers in some mountain belts. It makes up 1% of the Earth’s volume.

Continental crust (SIAL, Silicon and aluminium)

Average rock density about 2.7 g/cm3

Its density varies between 2.0 to 2.8 g/cm3

Composed of silicon and aluminium

Floats higher on the mantle forming the land masses and mountains. It is 30 to 70 km thick.

Oceanic crust (SIMA), silicon and magnesium)

Oceanic crust ranges from 3 to 15 km thick

Density vary between 3.0 to 3.1 g/cm3

Floats lower on the mantle forming the oceanic basins. It is about 8 km thick.

 Mantle – a solid rocky (silica-rich) shell that extends to a depth of about 2900 kilometers. It makes up 83% of the Earth’s volume

The mantle can further be dived into:

(i) Upper layer of mantle (Asthenosphere)

(ii) Transition layer and,

(iii) Lower layer of mantle (Mesosphere)

Upper mantle is a rigid layer of rock with average density 3.3kgm-3

Transition layer is the layer that separates upper and lower mantle.

Lower mantle plays an important role in tectonic plate movement which creates earthquakes and volcanoes.

Its density is about 5.7 kgm-3

Note:
The mantle rocks are said to be in a plastic state.

The upper part of a mantle has a temperature of about 870C. The temperature increases downwards through the mantle to about 2200C near the core.

 Core – an iron – rich sphere having a radius of 3486 kilometers making up 16% of the Earth’s volume

The core is divided into two parts:

(i) Outer core

(ii) Inner core

i. Outer core is a liquid of molten iron and nickel alloys. The Earth’s magnetic field is generated within the outer core due to convective. It is 2270 kilometers thick.

ii. Inner core is a solid iron and nickel alloys. The temperature within the inner core is higher than the outer core but the inner core is solid, this is because higher pressure in this region causes the melting point to rise. It is a sphere of radius of 1216 kilometers.

Average density is nearly 11 gcm-3and at Earth’s center.

Layers defined by physical properties

Lithosphere (sphere of rock)

Earth’s outermost layer

Consists of the crust and uppermost mantle

Relatively cook, rigid shell

Averages about 100 kilometers in thickness, but may be 250 kilometers or more thick beneath the older portions of the continents

Asthenosphere (weak sphere partially molten)

Beneath the lithosphere, in the upper mantle to a depth of about 660 kilometers

Small amount of melting in the upper portion mechanically detaches the lithosphere from the layer below allowing the lithosphere to move independently of the asthenosphere i.e. allows tectonic plate movement.

Mesosphere or lower mantle

Rigid layer between the depths of 660 kilometers and 2900 kilometers

Earth’s major boundaries

Discontinuity is the name given to any surface that separates one layer from another layer of the Earth.

The Moho (Mohorovicic discontinuity)

Discovered in 1909 by Andriaja Mohorovicic

Separates crustal materials (crust) from underlying mantle.

Gutenberg discontinuity

 Discovered in 1914 by Beno Gutenberg

 Is the boundary between the outer and inner core.

The Earth’s Structure

TEMPERATURE INSIDE THE EARTH

Earth’s temperature gradually increases with an increase in depth at a rate known as the geothermal gradient.

Temperature varies considerably from place to place

Averages between about 20C and 30C per kilometer in the crust (rate of increase is much less in the mantle and core)

The rate of heat flow within the Earth depends on:

(i) The thermal conductivity of the rock,

(ii) Temperature gradient of the rock

Sources of heat Energy within the Interior of the Earth

Major processes that have contributed to Earth’s internal heat include:

1. Heat emitted by radioactive decay of isotopes of uranium (U), thorium (Th), and potassium (K).

2. Heat released as iron crystallized to form the solid inner core.

3. Heat released by colliding particles during the formation of Earth.

4. Gravitational work done by the Earth due to its rotation through its own axis.

5. Electron motion in the core behaves like an electric current.

Heat Lost by the Earth

Heat in the earth is transferred by the process of;

(i) Convection and

(ii) Conduction

In the solid inner core and in the Earth’s crust heat is transmitted by conduction process. Rates of heat flow in the crust vary.

In the Mantle heat is transmitted by conduction process. Rates of heat flow in the crust vary.

In the Mantle heat is transmitted by convection process. There is not a large change in temperature with depth in the mantle.

Mantle must have an effective method of transmitting heat from the core outward.

Transfer of heat in the Earth by mantle convection

Uses of the Mantle

1. The mantle transfers heat by convection from the earth’s crust to the out regions of the earth and thus help it to regulate its temperature

2. The upper part of the mantle is molten, this allows tectonic plates movements.

EARTHQUAKES

An earthquake is a sudden motion or shaking of the earth caused by a sudden release of energy that has accumulated within or along edges of the earth’s tectonic plates.

Earthquakes occur within the Earth’s crust along faults that suddenly release large amounts of energy that have built up over long periods of time.

The shaking during an earthquake is caused by seismic waves.

Seismic waves are propagating vibrations that carry energy from the source of the shaking (earthquake) outward in all directions.

Seismic waves are generated when rock within the crust breaks, producing a tremendous amount of energy. The energy released moves out in all directions as waves, much like ripples radiating outward when you drop a pebble in a pond.

CAUSES OF EARTHQUAKES (SEISMIC WAVES)

The main causes of the Earthquakes and so seismic waves are:

1. Movement of tectonic plate.

2. Volcanic activity.

3. Landslide and avalanches.

4. Rebound of the crust.

5. Human activities.

Movement of tectonic plate

The Earth’s crust is made up of segment (layers) called tectonic plates which are slowly drifting in various directions. Tectonic plates may create a fault.

A boundary is a line where two tectonic plates meet.

A geologic fault is a fracture in the earth’s crust causing loss of cohesion and accompanied by displacement along the fracture.

How an earthquake is formed

Tectonic plates grind past each other, rather than slide past each other smoothly. As the plates move past each other they can become locked together due to friction. For some time, they don’t move and strain energy builds up. Stresses builds between them until fractional force holding the plates together give away. The plates move suddenly, releasing the energy and then held again. This sudden jerk is what is felt as an earthquake.

Note

(a) The Earth’s crusts near tectonic plate edges are forced to bend, compress, and stretch due to the internal forces within the earth, causing earthquakes.

(b) Nearly all earthquakes occur at plate boundaries.

Volcanic activity

Molten rock “magma” from the mantle is forced through a weak point in the Earth’s crust creating a volcanic eruption. When magma reaches the Earth’s surface it is known as “Lava”. Successive eruptions leads to the buildup of lava on the sides of the vent creating the familiar “cone – shape” of a volcanoes

Earthquakes may be created by the violent explosions which occur if there are sudden movements of the magma.

Landslides and avalanches

A landslide occurs when a large mass of land slips down a slope. An Avalanche occurs when a large mass of snow pours down a mountain side. Both of these effects can start an earthquake

Rebound of the crust

Elastic rebound theory state that “as tectonic plates move relative to each other, elastic strain energy builds up along their edges in the rocks along fault planes”. Since fault planes are not usually very smooth, great amount of energy can be stored (if the rock is strong enough) as movement is restricted due to interlock along the fault. When the shearing stresses induced in the rocks on the fault planes exceed the shear strength of the rock, rupture occurs.

It follows from this that if rocks along the fault are of a certain strength, the fault is a certain length, and the plates are slipping past each other at a defined rate, it is possible to calculate the amount of time it will take to build up enough elastic strain energy to cause an earthquake and its probable magnitude.

When a fault breaks it release elastic strain energy it stored, and hence earthquake.

Human activities

Human activities such as those caused by nuclear bombs can create earthquake, together with mine actives.

EARTHQUAKE TERMS

Energy released by an earthquake moves outwards from the origin in the form of concentric waves.

Focus (Hypocenter) is the point in the Earth where seismic waves originate.
Epicenter is the point on the earth’s surface vertically above the focus.

Hypocentral distance is the distance between the focus and the seismic detection station.

Epicentral distance is the distance between the epicentral and the seismic station.

S = Seismic station

E = Epicenter

ES = Epicentral distance

TYPE OF SEISMIC WAVES

i. Seismic waves are elastic waves that propagate within the earth.

There are two type of seismic waves:

1. ii. Body waves, spread outward from the focus in all directions.

2. iii. Surface waves (Long, L – waves) spread outward from the epicenter to the Earth’s surface along the crust, similar to ripples on a pond. These waves can move rock particles in a rolling motion that very few structures can withstand. These waves move slower than body waves.

BODY WAVES

There are two types of Body Waves

(1) Primary P – wave and

(2) Secondary, S – waves

1. 1. Primary Wave (P – wave): Are longitudinal (compression) wave (travels in the same direction the waves move)

Characteristics of P – waves

1. Are the fastest seismic waves (7 – 14 km/second). Arrives at recording station first, hence the name primary means first.

2. Can pass through solid, gas and liquid, hence can pass through crust, mantle and the cores.

3. Are longitudinal compression waves. The rocks that transmit the P – waves are alternately compressed and expanded.

Velocity of P – waves

The velocity of primary waves depends on the density,bulk modulus B and the shear modulus

In solid, =

In liquid =

A fluid cannot support shear stresses hence

2. Secondary Wave (S – wave): Are transverse (shear) wave (travels perpendicular to the wave movement).

Characteristics of S – waves

1. i. Slower moving (3.5 – 7 km/second) hence are detected after primary waves.

2. ii. Caused by a shearing motion

3. iii. Cannot pass through a fluid (gas or liquid) because they are transverse. Hence are unable to pass through the liquid outer core.

Velocity of S – waves

The velocity of shear waves depends on the density and the shear modulus

In solid, =

In liquid =

Note: Since the density and states of the earth layers varies, the speed of the seismic waves also vary from layer to layer, the solid part showing greater speed and the liquid ones lower speed.

Primary wave and secondary wave

SURFACE WAVES/LONG WAVES

Surfaces waves are produced when earthquake energy reaches the Earth’s surface.

These are the slowest moving waves, but are the most destructive for structures on earth

There are two types of L – Waves:

(i) Love long waves

(ii) Rayleigh long waves

i. Love Waves

Love waves are Transverse horizontal motion, perpendicular to the direction of propagation and generally parallel to the Earth’s surface.

They are formed by the interaction of S waves with Earth’s surface and shallow structure and are dispersive waves. The speed at which a dispersive wave travels depends on the wave’s period.

Characteristics of Love Waves

1. i. Love waves are transverse and restricted to horizontal movement (horizontally polarized).

2. ii. The amplitude of ground vibration caused by a Love wave decrease with depth. The rate of amplitude decrease with depth also depends on the period/frequency.

3. iii. Loves wave are dispersive, i.e. wave velocity is dependent on frequency; low frequency – higher velocity.

4. iv. Speed of love waves is between 2.0 and 4.4 km/s

5. v. Love waves travels within the earth’s crust only.

LOVE WAVE

Rayleigh Waves

Rayleigh waves are vertically polarized long waves. The slowest of all the seismic wave types and in some ways the most complicated.

Characteristics of Rayleigh Waves

1. Rayleigh waves are transverse and restricted to vertical movements (vertically polarized).

2. The amplitude of Rayleigh wave decreases with depth. The rate of amplitude decrease with depth depends on the period/frequency

3. Rayleigh wave are dispersive, i.e. wave velocity dependent on frequency; low frequency – high velocity

4. Speed of love waves is between 1.0 and 4.2 km/s slowest of all waves.

5. Travels within the earth’s crust only.

6. Depth of penetration of the Rayleigh waves depend frequency, with lower frequencies, penetrating greater depth.

PROPAGATION OF SEISMIC WAVES

Like all other types of waves, seismic waves may undergo,

(i) Reflection, (ii) Refraction, (iii) Dispersion, (iv) Diffraction, (v) Attenuation.

Seismic reflection:
Seismic waves bounce (reflect) rock boundaries of different rock type (density).

Seismic refraction:
Waves change velocity and direct (refract) when they enter a medium of different density it the one they just passed through.

Seismic Dispersion:
surface waves are dispersive which means that different periods travel at different velocities. The effects of dispersion become more noticeable with increasing distance because the long travel distance spreads the energy out (it disperses to energy).

SEISMIC WAVE PATHS

By comparing the data recorded by many stations all over the world the nature, speed and the paths of the seismic waves can be determined. This information can be used to tell us about the earth’s interior such as density sand state in each layer.

L – Waves travel within the Earth’s crust only

P and S waves travel through the earth in a curve path. The waves are refracted because their speeds a constantly changing with depth due to continue increase in density. Waves are also strongly refracted the Mantle – Core boundary.

Surface waves travels through the Earth crust only

Shadow zone is the region on the Earth’s surface where no S or P waves are present.

This lies between 105 and 140. Only surface waves may be detected in this region.

Shadow zone occurs because:

(i) P – Waves are strongly refracted at the liquid outer core.

(ii) S – Waves can’t travel through the liquid outer core.

Seismic waves can also be used to locate the discontinuities in the earth’s crust. A change in density or crack would affect the propagation of the waves.

This alteration in the wave’s path or speed would indicate the discontinuity.

The fact that S waves do not travel through the core provides evidence for the existence of a liquid layer beneath the rocky mantle.

The change in the velocity of P waves at crust – Mantle boundary reveals the presence of Mohorovicic discontinuity

P waves passing through the inner core show increased velocity suggesting that the inner core is solid.

Both P and S – Waves slow down when they reach the asthenosphere. Because of this scientists know that the asthenosphere is partially liquid

MEASUREMENTS OF EARTHQUAKES

i. Seismology is the scientific study of earthquakes (seismic waves) and artificially produced vibrations in the earth.Seismograph is a sensitive instrument that is used to record earthquakes and seismic waves (i.e. ground movements).

ii. Seismogram is the record of ground movement drawn by a seismograph.

The arrival of seismic waves at a station

The recording of the motion caused by seismic waves can be done by using;

(a) Mechanical method, as in the drawing above.

( (b) Optical method, where light is used to write the motion on a photosensitive paper instead of using a pen.

(c) Electronic method, where a coil is fixed to the mass of the pendulum and moves in a magnetic field. This induces a voltage which is amplified so that they can be easily interpreted.

Seismometers record both the magnitude and intensity of the earthquake.

LOCATING THE EPICENTRE

Although S – waves, P – waves and surface waves all start out at the same time, they travel at different speeds. The speed of a traveling seismic wave can be used to determine the location of an earthquake epicenter.

A seismograph records the arrival time and the magnitude of horizontal and vertical movements caused by an earthquake. The arrival time between different seismic waves is used to calculate the travel time and the distance from the epicenter.

The difference in arrival time between primary waves and secondary waves is used to calculate the distance from the seismograph station to the epicenter.

It is crucial that seismic waves are recorded by three different seismograph stations in order to estimate the location of the epicenter.

(i) Locate at least 3 stations on a map that recorded the seismic waves.

(ii) Calculate the time difference between arrival of P – waves and arrival of S – waves from a seismogram. The time difference is proportional to the distance from the epicenter. Because the direction to the epicenter is unknown, the distance defines a circle around the receiving station. The radius of each circle equals that station’s distance from the earthquake epicenter.

SIZE OF AN EARTHQUAKE

The size of an earthquake can be measured in terms of its intensity (Mercalli/Wood Neumann scale) or its magnitude (Richter scale).

Mercalli Intensity Scale

The Mercalli scale measures the intensity of how people and structures are affected by the seismic event. In essence, it measures damage. It is much more subjective and uses numbers ranging from 1 (no damage) to 12 (total destruction).

ISOSEISMAL LINES

Intensity distribution maps can be drawn up showing the intensities of an earthquake over a region. The earthquake is most intense at the epicenter and decreases with distance.

Isoseismal lines are line joining points of equal intensity.

Richter magnitude scale

The magnitude of an earthquake is measured in terms of energy released by an earthquake. This is determined from the amplitude of the seismic wave recorded on a seismogram 100 km from the epicenter. The magnitude is equal to the logarithm of the amplitude. Therefore each successive number represents a tenfold (x10) increase in the ground motion. The Richter scale starts at 0 but has no upper limit. -However 8 represent an earthquake that causes total destruction within the region.

Intensity of an earthquake is a measure of its strength based on the changes it causes to the landscape.

EARTHQUAKE PREDICTIONS (WARNINGS)

Forecasting (predicting) earthquakes is very difficult, although there are a number of warning signs which occur before an earthquake happens.

(i) Change in the velocity of p – waves.

(ii) Electrical resistivity of the rocks decreases.

(iii) An increase in radon, emission (radon is an inert gas, radon is found to increase in soil and water samples).

(iv) Increase in fore shock (small tumors that occur just before an earthquake).

(v) Local variations in the magnetic field.

(vi) Animals begin to behave strange.

(vii) Water levels rise or fall in wells few days before earthquake.

(viii) Increase in temperature of the area few months before the occurrence of an earthquake

PRECAUTIONS

Some of the world’s populations are living in regions where there is a high risk of an earthquake. Most of these regions lie along fault lines. However a few precautions can be taken to reduce the damage caused.

(a)Build structures that can withstand the forces of an earthquake. One method is to include shock absorbers into the buildings foundations.

(b)Scientific research has shown that pumping water out of the earth reduces the stress in the crust hence preventing an earthquake. However this technique is very expensive.

(d) If you are inside a house, stay in a safe place where things will not fall on you.

EARTHQUAKE HAZARDS

Earthquake give rises to a number of hazards which pose a great risk to human life, animals, property and the environment at large. The following are some hazards:

1. Landslides and avalanches: The shaking caused by an earthquake can cause unstable hillsides, mountain slops’ and cliffs to move downwards creating landslides. Earthquakes can also trigger avalanches on snow slopes

2. Tsunamis: If an earthquake occurs under the sea or ocean, the shock waves disturb the water. The ocean floor can rise or fall causing the water to rise and fall too. This movement creates huge water waves called tsunamis that travel across the ocean.

3. Collapsing building: Buildings or structures may collapse during a strong earthquake. The collapse of the building may kill people.

4. Fire outbreak: Earthquakes can cause gas or oil pipes to break and or the collapse of electricity lines. This may set up fire.

5. Backward rivers: Tilting ground due to earthquakes can make rivers change their course.

REFLECTION SEISMOLOGY

This is the study of reflection of seismographic waves by different materials inside the earth.

Applications:

(i) Location of underground oil and water

(ii) Locate discontinuities within the earth

SEISMIC PROSPECTING

Seismic prospecting is the sending of seismic waves into the deep earth’ crust in order to study the structure of the earth or detecting oils or gases in the interior of the earth by utilizing the property of reflection and refraction of the seismic waves.

THE EARTH’S MAGNETIC FIELD

The earth has a weak magnetic field, 95% of this field is created inside the Earth’s core 5% is the result of atmospheric effects above the Earth’s surface.

Geomagnetism is science of study of the earth magnetic field, its causes and its variations.

Generation of the Earth’s magnetic field within the core

The accepted explanation for the origin of the Earth’s magnetic field within the core is given by Lemoir’s self exciting dynamo theory.

The Earth’s Outer Core consists of molten conducting metals (Iron and Nickel) which are rich in free electrons. The Earth’s rotation causes the molten metal to rotate and hence large convection currents are set up within the outer core. These currents generate a magnetic field.

Eddy currents are now generated due to a conducting material moving in a magnetic field. These Eddy currents modify the position of the Earth’s magnetic field so that it does not lie along the Earth’s axis of rotation. The present magnetic poles are situated 800km from the Earth’s axis.

Generation of magnetic field in the Atmosphere

In the Earth’s atmosphere there is a region know as the ionosphere which consists of free electrons and ions. The movement of these charges creates a magnetic field. This effect provides a small fraction of the Earth’s total magnetic field.

TERMS ASSOCIATED WITH THE EARTH’S MAGNETIC FIELD

Magnetic meridian: A vertical plane passing through the axis of a freely suspended magnetic needle.

Geographic meridian: A vertical plane passing through the geographic axis.

Magnetic equator: Is the locus of points on earth’s surface where the needle (free to rotate in a vertical plane) remains horizontal.

The Earth’s magnetic field pattern is similar to that produced by a giant bar magnet or solenoid.

Note: (i) The magnetic North pole which lies in the Northern Hemisphere behaves like a south pole or a bar magnet, i.e. the field lines are directed towards it.

(ii) The magnetic south pole which lies in the southern hemisphere behaves like a north pole of a bar magnet, i.e. the field lines are directed away from it.

ELEMENTS OF EARTH’S MAGNETISM

Angle of variation of declination, at a place is the angle between the geographic meridian and the magnetic meridian at that place.

Angle of dip or declination, at a place is the angle between the directions of intensity of the earth’s total magnetic field declinationand the horizontal direction, in the magnetic meridian at that place.

Horizontal component of Earth magnetic field It is the component of the Earth’s total magnetic field along the horizontal direction in the magnetic meridian.

VARIATIONS OF THE EARTH’S MAGNETIC FIELD

The Earth’s magnetic field is not constant but varies continuously with time.

(i) Short term variations (Irregular changes): The magnetic field changes daily due to variations in the magnetic field created in the ionosphere. The charged particles in this region of the atmosphere are affected by the Sun’s gravitational pull (which is stronger when the sun is directly above that area)

Also during periods of high solar activity charged particles from the solar wind are able to penetrate the magneto pause and arrange themselves under the influence of the magnetic field in a formation called Van Allen Belts.
These charged particles cause further Eddy currents within the ionosphere, altering the Earth’s magnetic field strength.

Solar wind is a continuous stream of moving electrons and protons in the atmosphere which are produced from flare (eruptions) from the sun. Normally these charged particles move from west to south at 300 – 500 km/s.

Magnetic storm is a sudden worldwide disturbance of the earth’s magnetic field caused by dynamic interaction of the earth’s magnetic field and the sun. During magnetic storm, the earth’s magnetic field is unusually active.

Effects of Magnetic Storm

(a) Large storms can cause the loss of radio communication

(b) Damage satellite electronics and affect satellite operations.

(d) Induce voltage surges in electric power grids causing blackouts.

(e) Reduce the accuracy of global positioning systems.

(ii) Long term variations (Secular changes): The Earth’s magnetic field position is constantly changing, now the magnetic North pole is moving at 8 km per year, and the magnetic South Pole at 16 km per year.

Evidence from the alignment of magnetized rocks layers in the Earth’s crust show that the Earth’s magnetic field has actually reversed in direction several times during the Earth’s history (i.e. the direction of the fields have reversed causing a north acting pole to become a south acting pole.) The present polarity of the Earth’s magnetic field has not changed for 700,000 years.

VAN ALLEN BELTS

The Van Allen belts consist of two regions of highly charged particles which are trapped within the Earth’s magnetic field:

Inner Belt consists of protons and positive charged particles

Outer Belt consists of electrons and negatively charged particles.

THE ATMOSPHERE

Earth’s atmosphere is divided into five main layers, the exosphere, the thermosphere, the mesosphere, the stratosphere and the troposphere. The atmosphere thins out in each higher layer until the gases dissipate in space. There is no distinct boundary between the atmosphere and space, but an imaginary line about 110 kilometers from the surface, called the Karman line, is usually where scientists say atmosphere meets outer space.

TROPOSPHERE

The troposphere is the layer closest to Earth’s surface. It is 10 km thick and contains half of Earth’s atmosphere. Air is warmer near the ground and gets colder higher up. Nearly all of the water vapor and dust in the atmosphere are in this layer and that is why clouds are found here.

Lapse rate is the rate of fall of temperature in degrees per kilometer rise. It has an average value of 6 C per km in the troposphere.

Tropopause is the upper boundary of the troposphere.

Importance (uses) of troposphere

1. Controls the climate and ultimately determines the quality of life in the atmosphere.

2. It supports life on earth. It contains oxygen which is used to respiration by animals.

STRATOSPHERE

The stratosphere is the second layer. It starts above the troposphere and ends about 50 km above ground.

The temperature of the stratosphere slowly increases with altitude. This temperature increase is due to the presence of Ozone layer which absorbs heat from the sun in the form of ultraviolet light.

The Ozone layer occupies the middle of stratosphere between 20 and 30 km it consists of Ozone formed by oxygen molecules dissociated and reforming into 03.

The air here is very dry, and it is about a thousand times thinner here than it is at sea level. Because of that, this is where jet aircraft and weather balloons fly.

Stratopause is the upper boundary of the stratosphere.

Importance (uses) of stratosphere

The stratosphere prevents harmful ultraviolet radiation from reaching the earth. Ozone absorbs harmful radiation from the sun. The Ozone protects plants and shield people from skin cancer and eye cataracts.

MESOSPHERE

The mesosphere starts at 50 km and extends to 80 km high. The top of the mesosphere, called the mesopause, is the coldest part of the Earth’s atmosphere with temperatures averaging about – 90C. The temperature of the mesosphere decreases with altitude (because there is no ozone to absorb heat).

This layer is hard to study. Jets and balloons don’t go high enough, and satellites and space shuttles orbit too high. Scientists do know that meteors burn up in this layer.

Importance of mesosphere

Mesosphere, thermosphere and exosphere prevent harmful radiation such as cosmic rays from reaching the earth surface.

THERMOSPHERE

The thermosphere extends from about 80 km to between 500 and 1,000 km. Temperatures increases as it approaches nearer to the sun. The heating effects of the earth no longer exist at these higher altitudes.

The thermosphere is considered part of Earth’s atmosphere (the upper atmosphere), but air density is so low that most of this layer is what is normally thought of as outer space. In fact, this is where the space shuttles flew and where the International Space Station orbits Earth.

This is also the layer where the auroras occur. Charged particles from space collide with atoms and molecules in the thermosphere, exciting them into higher states of energy. The atoms shed this excess energy by emitting photons of light, which we see as the colorful Aurora Borealis and Aurora Australis.

EXOSPHERE

The exosphere, the highest layer, is extremely thin and is where the atmosphere merges into outer space. It is composed of very widely dispersed particles of hydrogen and helium.

The upper part of the exosphere is called Magnetosphere. The motion of ions in this region is strongly constrained by the presence of the earth’s magnetic field. This is the region where satellites orbit the earth

Note:

(i)The troposphere, stratosphere, and mesosphere are collectively forms the homosphere. These layers have the same chemical composition; 78% nitrogen, 21% oxygen, 1% argon and other gasses which sum to about 0.05%. The thermosphere is excluded due to different in chemical composition.

(ii) The upper atmosphere above 90 km is called heterosphere. The atmosphere is no longer a mixture of gases but separates into layers heavier ones forming the bottom layer.

VARIATION OF TEMPERATURE WITH HEIGHT

The temperature above the Earth surface varies as shown in the graph below.

The residence time, is the mean lifetime of a gas molecule in the atmosphere

THE IONOSPHERE AND TRANSMISSION OF RADIO WAVES

The ionosphere is the region containing high concentrations of charged particles ions and electrons.

The ionosphere is created by atoms absorbing U.V radiation, gamma and X – rays.

The ionosphere extends from the lower thermosphere 55 km to 550 km above the earth’s surface.

Ionosphere layers:

Due to difference in composition of the air in the ionosphere, the ionosphere is divided into layers.

(i) The lower layer, called D layer; this layer exists only in the day time at an altitude of 55 to 90 km above the earth’s surface. Ionization in this region is relatively weak.

(ii) The next layer, E – layer: this layer is between 90 and 145 km above the earth’s surface. It has a maximum density at noon but is only weakly ionized at night.

(iii) The top layer, the F – layer: At night exists as a single layer in a region of about 145 to 400 km above the earth’s surface. During the day it splits into two layers, F1 and F2.

The Ionosphere and Communication

The ionosphere plays an important role in communication. Radio waves can be reflected off the ionosphere allowing radio communications over long distances. However this process is more successful during the night – time.

Why Transmission is better at Night?

During the day: the ionosphere extends into lower atmosphere (D layer). In this layer there is high concentration of particles and so recombination of electrons and ions due to collision is more likely to occur. The leads to the radio waves being absorbed rather than reflected. Hence distant communications are poor during the day.

During the night: The D layer disappears due to decrease in ionization of molecules but recombination of electrons and ions still occurs at a fast rate. The radio waves are then reflected by E and F layers in which recombination of electrons and ions is rare hence there is less absorption of the radio waves.

EXAMPLES: SET C

Example 01: Necta 1985 P1

(a) (i) Distinguish between P and S waves, state clearly the difference between their speeds in a medium.

(ii)Draw a schematic diagram showing how one station on the Earth’s surface can receive P or S waves from a distant source and state which waves can be refracted by the Earth’s outer core.

(b) (i) Give a summary of the origin and composition of the ionosphere.

(ii) What is the net electric charge in the ionosphere?

(iii) Show graphically how electron density changes with altitude in the ionosphere.

Answers

(a) (i) P – waves are longitudinal compression waves which can pass through solid, gas and liquid, whereas S – waves are transverse shearing waves which cannot pass thorough a fluid (gas or liquid)

The speed of P – waves in a medium is approximately twice that of the S – waves hence P – waves are faster than S – waves.

(ii) Refer the diagram for the seismic wave paths

(b) (i) Ionosphere is the upper part of the atmosphere. The ionosphere is formed due to the ionization of gaseous atoms as they absorb ultraviolet radiation from the sun, gamma and X-rays.

(ii) The net electric charge in the ionosphere is zero.

(iii) Variations of electron density in the ionosphere Electron density increases from D to F layer

Example 02: Necta 1988/1993 P1

(a) What are the factors that influence the velocities of P – and S – waves?

(b) Explain briefly the characteristics property of seismic waves which is used to locate discontinuities in the earth’s crust.

Answer

(a) The velocities of both P and S – waves are influenced by;

(i) Density of the rock material (Media),

(ii) Moduli of elasticity.

(b) Speed is the characteristic property of seismic waves that is used to locate discontinuities

Between the crust and mantle there is abrupt change of density, which shows an abrupt change in speed of both P – and S – waves, a Mohorovicic discontinuity exists here. Both P – and S

waves travels across this discontinuity.

Between the mantle and the core there is the Gutenberg discontinuity only P – waves travel this discontinuity.

Example 03: Necta 1989 P1

(a) State three sources of heat energy in the interior of the earth.

(b) (i) How does temperature vary with depth of the Earth?

(ii) What are the factors that influence the flow of heat from the interior of the Earth?

Answers

(a) Refer notes

(b) (i) The temperature increases with increasing depth

(ii) The rate of heat flow (conduction) is given by

The heat flow from the interior of the earth depends on:

Thermal conductivity of the rock,

Temperature gradient of the rock

Example 04: Necta 1989 P2

(a) What do you understand by the terms?

(i) Solar wind,

(ii) Magnetopause

(iii) Magnetosphere?

(b) What are the various factors that contribute to the Earth’s magnetic field?

(c) (i) With the aid of a suitable diagram, illustrate the components of the earth’s magnetic field at a given point P in the earth’s atmosphere.

(ii) An electron whose kinetic energy is 10 eV is circulating at right angles to the earth’s magnetic field whose uniform induction is 1.0 x 10 Wbm-2. Calculate the radius of the orbit and its frequency in that orbit.

Answers

(a) (i) Solar wind is a continuous stream of fast moving charged particles in the atmosphere which are produced from flare (eruptions) from the sun:

(ii) Magnetopause is the upper boundary of the magnetosphere.

(iii) Magnetosphere is the upper most part of the exosphere consisting mainly of charged ions. These particles move under the influence of the earth’s magnetic field.

(b) Short term variations: Disturbances in the magnetosphere due to solar emissions, these charged ions travel and in the ionosphere they form ring currents which give rise to a magnetic field.

Long term variations: The molten inner core of the earth is partly ionized. The movement of this ionized core causes a magnetic field which contributes to the earth’s magnetic field.

Example 05: Necta 1990 P1

(a) Define the term “isoseismal line”.

(b) Write short notes on each of the following regions of the atmosphere.

(i) Troposphere, (ii) Stratosphere, (iii) Exosphere

Answer: Refer notes

Example 06: Necta 1990 P2

(a) Explain clearly how P and S – waves were used to ascertain that the outer core of the earth is in liquid form.

(b) Giving reasons, discuss the temperature variation in atmosphere (above the earth’s surface).

Answers

(a) P – waves are longitudinal elastic, waves capable of passing through solids and liquids and S – waves are traverse elastic waves capable of a travelling through solids only.

As both waves are projected towards the surface from interior core only the P – waves are recorded. This shows that the outer core is in liquid form.

(b) From the ground level, the atmospheric temperature decreases steadily as altitude increases steadily as altitude increases up to the troposphere. Thereafter the temperature increases with altitude up to the stratosphere. The ozone of the stratosphere absorbs the incoming sun radiation hence the temperature increases. In the mesosphere there is no ozone thus there is a decrease (cooling) with increasing altitude. The heating effect of the earth ceases in the thermosphere so, the closer to the sun, the higher graph refer notes.

Example 07: Necta 1991 P2

(a) List down four physical changes that took place at a location just before onset of an earthquake at that particular location.

(b) Give brief accounts of the processes that give rise to:

(i) The earth’s magnetic field,

(ii) Volcanic eruptions

Answers

(a) Density of rocks, stresses faults and waves

(b) (i) Explain generation of the earth’s field in the atmosphere and the outer core.

(ii) The seismic or earthquakes waves result from a fracture or sudden deformation of the earth’s crust. Vast stresses do occur locally in the rocks being concentrated where the rocks are sliding over one another. In regions where pressure is reduced, pockets of molten rock called magma are formed. Once the rock has melted the pressure may force it into cracks and fissures in the surrounding solid rock. This may emerge above the surface as a lava flow or volcano.

Example 08: Necta 1992 P1

(a) What do you understand by the term ionosphere?

(b) Explain how short wave long distance transmission and reception of radio waves is more effective at night than it is during the day time.

Answer

(b) In the day time, the base of the ionosphere (D-layer) is at lower heights where the high concentration of particles allows for ionization and recombination of ions by collision. Because of this, radio waves are absorbed rather than reflected, so distance communication is poor.

During the night time, the D – layer disappear, the base of the ionosphere is higher thus the recombination of ions is rare and so less absorption of waves occurs. Obliquely transmitted waves therefore can be reflected for distant reception.

Example 09: Necta 1993 P2

(a) What is the origin of the earth’s magnetic field?

(b) The diagram below shows the structure of the Earth. Name the parts indicated by the letter A to F.

Answer

(b) A represents Mohorovicic discontinuity

B represents Gutenberg discontinuity

C represents core

D represents Mantle

E represents Epicenter

F is not clear to interpret.

Example 10: Necta 1994 P1

(a) Define the terms: angle of inclination (dip) and angle of declination (variation) as used in specifying the earth’s magnetic field at any point.

(b)The earth’s total resultant flux density BR in a certain country is found to be 5.0 x 10-5 T and the horizontal component is BH is 2.0 x 10-5 T. Calculate ;

(i) The vertical component, Bv, and

(ii) The angle of inclination in that country

Answers

(a) Refer notes

(b) A = Earth’s surface, B = Crust, C = Moho discontinuity, D = Gutenberg discontinuity, E = outer core, F = Mantle and G = inner core.

Example 17: Necta 1998 B

(a) Explain the following terms; Earthquake, Earthquake focus, Epicenter and body waves.

(b) List down three (3) sources of earthquakes,

(ii) Mention the ionosphere layers that exist during the day time

(iii) Give the reason for better reception of radio waves for high frequency signal of night than during day time.

(d) Explain briefly three different types of radio waves traveling from a transmitting station to a receiving antenna.

Answers

(a) Refer notes

(b) Refer notes

(ii) Refer Necta 1992 (b)

(d) Ground (surface wave)

Space wave

Sky waves) (refer telecommunication notes)

Example 18: nectar 2000 P1

(a) With reference to an earthquake on a certain point of the earth explain the terms ‘focus’ and ‘Epicenter’

(b) What is importance of the following layer of the atmosphere?

(i) The lowest layer

(ii) The ionosphere

(ii) Describe briefly the meaning and application of “seismic prospecting”.

Answers

(a) Refer notes

(b) (i) Importance of troposphere is supports life on earth

(ii) Ionosphere enhances communication over long distances.

(ii) Seismic prospecting is an artificial production of seismic waves purposely for searching underground fuels and oils or gases

Example 19: Necta 2001 P1

(a) (i) Define the terms “angle of declination” as used in the specification of the earth’s magnetic field at a point

(ii) The horizontal component of the earth’s magnetic field at a location was found to be 26.0 while the angle of inclination was Find the magnitude of the field and the vertical component of the field at the location

(b) (i) Define an earthquake

(ii) Distinguish between P and S waves. What factors influence their velocities?

Answers

(a) (i) Refer notes

(ii)

(b) The velocities of P and S waves are influenced by;

Density, of the media

Shear modulus, of the media, and

Bulk modulus, B of the media.

Example 20: Necta 2002 P1

(a) (i) What is the importance of ionosphere to mankind?

(ii) Explain why transmission of radio waves is better at night than at day time.

(b) (i) What is an earthquake?

(ii) Explain briefly any four (4) causes of earthquake

Example 21: Necta 2003 P2

(a) Explain the following:

(i) Earthquake (ii) Earthquake focus (iii) The epicenter.

(b) List down three sources of earthquake

(ii) State the ionosphere layer that exists during day time.

(iii) Give the reason for better waves reception for light frequencies signal at night than during the day time

Example 22: Necta 2004 P1

(a) (i) Explain the terms epicenter and focus as applied to earthquake.

(ii) State any four (4) indications that may predict the occurrence of an earthquake.

(iii) State and explain two variations of the earth magnetic field.

(iv) State one necessary precaution to be taken to people living in a region with a high risk of occurrence of earthquakes.

(b) Explain the following

(i) Solar wind (ii) Magnetopause (iii) Ionosphere.

Example 23: Necta 2005 P1

(a) Define the following terms

(i) Epicentral distance (ii) Body wave (iii) Seismograph

(b) (i) explain the meaning of reflection seismology state its application

(ii) Show how the magnetic field within the atmosphere is generated?

(ii) State their importance

Answers

(a) (i) Lowest layer of atmosphere is troposphere and that of the ionosphere is the D – layer.

Example 24: Necta 2006 P1

(a) (i) State two (2) ways by which seismic wave may be produced

(ii) What is seismic prospecting?

(b) (i) Discuss briefly the importance of the lowest layer of the atmosphere and the ionosphere.

(ii) Sketch the temperature against altitude curve for the atmosphere indicating the important atmospheric layers.

(iii)The average velocity of P – waves through the earth’s solid core is 8kms-1. If the average density of the earth’s rock is 5.5 x 103kgm-3 find the average bulk modulus of the earth’s rock.

Answer

(a) (i) Causes of an earthquake

(b) (ii) using the formula

Example 25: Necta 2007 P1

(a) (i) What are the differences between P and S waves?

(ii) Explain how the two terms of waves (P and S) can be used in studying the internal structure of the earth.

(b) Write short notes on the following terms in relation to the changes in the earth’s magnetic field; long term (secular) changes, short – period (regular) changes, and short – term (irregular) changes.

(ii) Give a summary of location, constitution and practical uses of the stratosphere, ionosphere and mesosphere.

Answers

(c) (i) Geomagnetic micro pulsation are small rapid changes in the earth’s magnetic field. They have periods between 0.2 second and 10 minutes and intensities less than 0.01% of the minimum field.

Example 26: Necta 2008 P1

(a) Define the following terms:

(i) Earthquake (ii) atmosphere

(b) Distinguish between body waves and surface waves that are produced by an earthquake.

(ii) Draw a well labeled diagram which shows the interior structure of the earth.

Example 27: Necta 2009 P1

(a) (i) What is meant by the shadow zone?

(ii) Why does the shadow zone occur?

(b) (i) Name the lowest layer of the atmosphere and the lowest layer of the ionosphere.

(ii) State the importance of each of these layers in b (i) above

(iii) Explain briefly the reason for better reception of radio waves for high frequency signals at night times than during day times.

Example 28: Necta 2010 P1

(a) (i) Explain the terms: earthquake, earthquake focus and epicenter.

(ii) Describe clearly how P and S waves are used to ascertain that the outer core of the Earth is in liquid form.

(b) (i) Define the ionosphere and give one basic use of it.

(ii) Why is the ionosphere obstacle to radio astronomy?

Example 29: Necta 2011 P1

(a) (i) Define the following terms: Geophysics, Atmosphere and Epicenter

(ii) Write down brief notes on the location, composition and importance of the following:

Troposphere, Stratosphere, Mesosphere and Thermosphere

(b) (i) Draw sketch diagram showing the working part of a Seismometer.

(ii) Explain how temperature varies with both altitude and depth of the Earth.

(iii) Write down two factors that governs heat flow from the interior of the Earth.

Example 30: Necta 2012 P1

(a) (i) Name three layers of the atmosphere

(ii) Describe any two major zones of the earth.

(b) (i) What are the factors that influence the velocities of P and S waves?

(ii) The P and S waves from an earthquake with a focus near the earth’s surface travel through the earth at nearly a constant speed of 8 km/s and 6 km/s respectively. If there is no reflection and refraction of waves how long is the delay between the arrivals of successive waves at a seismic monitoring station at 90 in the latitude from the epicenter of the earthquake?

Solution

(a) (ii) any two of core, mantle, crust, hydrosphere, atmosphere

(b) (i) the density of rock, moduli of elasticity of rock material.

(ii) Illustration (R = earth radius)

TRY YOURSELF

(a) (i) What are auroras?

(ii) Define the homosphere

(b) (i) What are the factors which contribute toward volcanic eruptions?

(ii) What are the effects of volcanic eruptions?

(iii) What are lahars?

Lahars are rapidly flowing mixtures of rock debris and water that originate on the slopes of a volcano. They are also referred to as volcanic mudflows or debris flow. Volcanic eruptions may directly trigger one of more lahars by quickly melting snow and on a volcano or eject water from a crater lake. The form in a variety of at always including through intense rainfall on loose volcano rock deposits and as a consequence of debris of debris avalanches

ENVIRONMENTAL POLLUTION

Pollution is the addition of unwanted materials or pollutants into the environment.

Pollutant is any substance that does not belong in the natural system and disrupts the natural balance.

Type of Environmental pollution

(a) Air pollution (atmospheric pollution)

(b) Water pollution (hydrosphere pollution)

(d) Noise pollution

(e) Thermal pollution

ATMOSPHERIC (AIR) POLLUTION

AIR POLLUTION
This is a form of environmental pollution caused by the release of gaseous materials and dust particles in the atmosphere. The main pollutants found in the air we breathe include, particulate matter, lead, ground-level ozone, heavy metals, sulphur dioxide, benzene, carbon monoxide and nitrogen dioxide

Causes of Air Pollution

Man made causes:

(i) Clearing (deforestation) and burning of vegetation. This releases carbon dioxide in the atmosphere and dust particles which may be carried by wind on bare land.

(ii) Burning of fuels: This releases green house gases in the atmosphere. Fuels are burnt in cars, power stations and industries.

(iii) Construction activities, like road, building, etc construction, can add dust particles in the atmosphere.

(iv) Automobile exhausts. Car, trains, etc burns fuels as they move his releases pollutant gases in the atmosphere.

(v) Smokes from industries also pollute the atmosphere.

(vi) Agriculture activities. The use of pesticide/insecticides pollutes the air.

(vii) Mining activities

Natural causes:

(a) Volcanic eruptions – release smoke and dust particles in the atmosphere

(b) Wind storms – carry land particles into the air

(c) Temperature inversion – the increase in temperature in the stratosphere causes high altitude particles to sink to the troposphere

WATER POLLUTION

Water Pollution is the degradation of water quality in a manner that disrupts/prevents its intended or original use.

Surface Water or Ground water may be polluted

Causes of water pollution

(i) Disposal of untreated sewage (industrial or hospital, etc) into the water bodies.

(ii) Wind may introduce dust particles into water from the land.

(iii) Agriculture activities near water bodies. Chemical used during farming may be taken to the water bodies by the rain water.

(iv) Oil spilt. The leakage of oil in under water oil pipe, leakage from boats, ships, etc pollutes the water.

(v) Fishing by using chemicals (dynamite fishing).

(vi) Volcanic activities along water bodies.

(vii) Quarrying along the coast.

LAND (SOIL) POLLUTION

Soil pollution is defined as the build – up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents which have adverse effects on plant growth and animal health.

A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil.

Causes of soil pollution

(a) Chemical from industries

(b) Acid rain – this increase soil acidity

(d) Mining activities – increase rock sediment into the soil.

NOISE POLLUTION

Noise pollution is any disorganized loud sound.

Causes of noise pollution

(a) Noise from factories and workshops

(b) Thunderstorm explosion of bombs

(d) Radio on large volumes

(e) Slamming of doors

THERMAL POLLUTION

Thermal Pollution is a form of environmental pollution caused by the release of waste heat into water or air

Causes of Thermal Pollution

(a) i. Hot gases released by industries and motor vehicles warm the environment.

ii. Hot wasteful liquid from industries pumped to a river, lake, or other waterway

Effects of thermal pollution

(a) Heat introduced into water can make the water so hot that no living thing can survive in it

(b) Hot gases introduced in the atmosphere leads to green house effects.

Solutions of thermal pollution

(a)One is a cooling pond into which heated waste water is released before it enters a natural waterway. The cooling pond permits evaporation of some water, carrying heat into the air and thus releasing cooler water into the waterway

(b)The cooling tower method – either wet or dry – which also transfers heat to the air. In both types, heated water is introduced into a tower through which air is blown, and some heat is passed to the air.

PARTICULATE MATTER IN THE ATMOSPHERE (AEROSOLS)

Particulate matter (aerosol) is the general term used for a mixture of fine solid particles and liquid droplets found in the air.

Haze aerosol is frequently encountered in optical studies and includes any airborne particles that affect visibility.

Classification of Particulate

Particulates matter are classified in accordance with its formation mechanisms

(i) Primary particles (ii) Secondary particles

Primary particles are directly emitted into the atmosphere from their sources while secondary particles are formed after chemical transformation of their gaseous precursors. Chemical reactions transform primary pollutants (emitted by the sources) to secondary pollutants that are formed within the atmosphere. Ozone, sulfate aerosols, nitrates, are examples of secondary pollutants.

Particulate matters in the atmosphere are categorized as:

(i) Minerals, 72 – 91%, e.g. soil particles, hematite, mica, and talc;

(ii) Combustion products, 1 – 10%, e.g. coal and oil soot, fly ash, burned paper.

(iii) Biological materials 2 – 10% e.g. pollen, spores, starch, plant tissues and diatoms

(iv) Miscellaneous matter, trace – 8% e.g. salt, rubber, iron/steel, paint pigment and humus

Dust refers to a relatively course range of solid particles (diameter, d >1pm), produced by disintegration of minerals or from re-suspension by wind when sun blasting of soil particles may often causes comminuting.

Smokes and fumes are fine particles formed from the gas phase by condensation. In the case of fume the particles are generally from 0.01 – 1 pm diameter, and are often observed as agglomerates of smaller particles. Suspended particulate matter < 15 pm and diameter is usually defined as smoke.

Mists and fogs are liquid droplets Mists (d > 40 pm) and fogs (d = 5 – 40 pm).

Advantages of particulate matter in the atmosphere

Aerosols acts as nuclei were water vapour collects during the formation of water droplets through condensation.

Disadvantages of particulate matter in the atmosphere

(a) Cause global warming

(b) Can block the atmosphere (impair visibility)

(d) Changing the timing and location of traditional rainfall patterns

(e) Can lead to development of heart and lung diseases.

TRANSPORT MECHANISMS OF ATMOSPHERIC POLLUTANT

The transport of pollutants by the wind

The three transport processes that influence the regional dispersion are;

(a) Wind speed (shear)

(b) Directional veer (change in direction fo wind), and

Wind shear: The vertical gradient of wind speed (i.e. wind shear is responsible for lagging of low elevation pollutants behind those in the upper layers.

Directional veer: The directional veer with height causes lateral displacement of a vertically uniform puff.

The eddy motion is the vertical transport of pollutants from region of high concentration to low concentration. Eddy motions are due to random vertical and horizontal fluctuations caused by thermal and mechanical turbulence.

Both the transport speed and direction for an air parcel vary from day to day.

Stratosphere – troposphere interchange

Temperature inversion at the tropopause causes an interchange of particulate matters between Stratospheres – troposphere boundary.

EFFECTS OF POLLUTION ON VISIBILITY

Atmospheric pollution results into a reduction in visual range in the atmosphere. The reduction is visual range caused by an increase in airborne particles that affects light scattering and attenuation involves both primary and secondary aerosols, and may be experienced in rural as well as urban area.

EFFECTS OF ATMOSPHERIC POLLUTION ON THE GLOBAL ALBEDO AND CLIMATE

Increases in particulate matter in the atmosphere may:

(a) affect cloud droplet formation and precipitation,

(b) Reduce the amount of solar radiation that reaches the ground

However, controversy still remains as to whether the presence of particulate material exerts a net warming or cooling effect to enhance or offset the global warming predicted from increases in CO2 and chlorofluoro methanes in the atmosphere. In addition, considerable changes in global and surface albedo have been caused by deforestation, salinization, and desertification.

Global warming is the increase of the average temperatures near or on the surface of the earth as a result of greenhouse effect.

GLOBAL WARMING

Global warming is the increase of the average temperatures near or on the surface of the earth as a result of greenhouse effect.

Greenhouse effect

Greenhouse effect is the process in which the emission of radiation by the atmosphere warms the earth’s surface.

Greenhouse gases include carbon dioxide, methane, chlorofluorocarbons and dinitrogen oxide.

When heat from the sun reaches the earth’s surface in form of sunlight, some of it is absorbed by the earth. The rest is radiated back to the atmosphere at a long wavelength than the incoming sunlight. Some of these longer wavelengths are absorbed by the greenhouse gases in the atmosphere before they are lost out of space. The greenhouse gases reflect the heat back to the earth and warm the environment.

Sources of greenhouse gases in the atmosphere

(a) Carbon dioxide is added in the atmosphere by:

(i) Clearing and burning of vegetation

(ii) Burning of fossil fuels

(b) Methane is added in the atmosphere by:

(i) Agricultural activities;

(ii) The mining of coal and oil

(i) Combustion of fossil fuels in vehicles and power station

(ii) Use of nitrogenous fertilizer, and

(iii) The burning of vegetation and animal waste

(d) Sources of chlorofluorocarbon include fridge, air conditioners and aerosols.

Effects of Global Warming

(a) Increase in the temperature of the oceans,

(b) Rise in sea levels,

(d) Acidification of the oceans,

(e) Extreme weather events like flood, droughts, heat waves, hurricanes and tornadoes

(f) Higher or lower agriculture yields,

(g) Melting of Arctic ice and snow caps. This causes landslides, flash floods and glacial lake overflow,

(h) Extinction of some animals and plant species,

(i) Increase in the range of disease vectors (organisms that transmit disease).

Solution to Global Warming

(a) Use of cleaner alternative sources of energy such as solar and wind,

(b) Put in place energy conservation measures to reduce the use of fossil fuel,

(a) Use of cleaner alternative sources of energy such as solar and wind,

NUCLEAR WASTE AND METHODS OF DISPOSAL

Nuclear wastes are the chemical products (solid, liquid and or gases) of nuclear reactions in the nuclear reactor.

Categories of radioactive waste

For the purpose of disposal, radioactive waste is divided into the following categories:

(a) High – level waste (HLW): spent fuel (SF) not destined for reprocessing; vitrified fission product solutions from reprocessing of spent fuel.

(b) Alpha – toxic waste (STW): waste with a content of alpha – emitters exceeding a value of 20,000 Becquerel’s per gram of conditioned waste.

Nuclear Waste Disposal

(a) Deep geological repository: for spent fuel and vitrified fission product solution product solutions from reprocessing. The products are buried deep into the earth.

(b) Recycling of the nuclear waste.

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Thanks for reading FORM SIX: PHYSICS STUDY NOTES-TOPIC 5: ENVIRONMENTAL PHYSICS

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Thursday, January 12, 2023

FORM SIX: PHYSICS STUDY NOTES-TOPIC 5: ENVIRONMENTAL PHYSICS

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