(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
(iii) Geophysics (Earth quakes)
Elastic rebound theory
Types of seismic waves
Propagation of seismic waves
(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.
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.
(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
(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.
(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
(a) Wind acts as pollinating agent for some plants and hence favours plant productivity.
(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
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.
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
Favourable humidity on plants help plants to conserve water for various activities and in seeds helps the development of new leaves.
Low humidity results into a greater rate of transpiration and hence may result into plant drying.
Effect of Air Temperature of Plant Growth
An Optimum temperature on plants enhances enzymic activities which in turn gives favourable conditions for plant growth.
(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 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:
(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.
(c) Soil Environment Components Which Influence Plant Growth
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,
(c) Organic matter (humus), 5% by volume,
(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.
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
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 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 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
(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)
(c) Explain briefly how soil temperature affects plant growth. (02 marks)
(b) Explain how the following climatic factors influence plant growth: air temperature, humidity, rainfall and wind. (06 marks)
(c) What are wind belts? Explain the effect of wind belts on plant productivity. (03 marks)
(a) What is mulching? (02 marks)
(b) Give two advantages and two disadvantages of mulching. (04 marks)
(c) Discuss the heating effect of solar radiation to plant growth. (04 marks)
(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)
(c) What is shading and what is its purpose? (03 marks)
(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)
(c) What are the advantages of wind breaks to plant environment? (03½ marks)
ENERGY FROM THE ENVIRONMENT
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
ii. Low grade energy is the one that is not easily transformed into anything else.
There are two types of energy sources, namely:
(i) Primary energy sources,
(ii) Secondary energy sources.
i. Primary energy sources
Primary energy sources fall into two groups:
(a) Finite energy sources,
(b) Renewable sources.
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.
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.
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)
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.
6. The available solar resource depends on two variables: The latitude at which the array is located and the average cloud cover.
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
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
K.E per second = =
The available wind power is P
(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:
Variations of power with wind speed
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.
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
5. Windmill generators don’t emit any emissions that can lead to acid rain or greenhouse effect.
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.
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
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:
(ii) Hot dry rock conversion
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 – 1000C.
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 2000C 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.
Uses of geothermal energy
Advantages of geothermal energy
2. New geothermal power plants currently generate electricity at low cost.
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.
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.
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.
Wave Energy Flux
Harvesting wave energy
There are two type of system:
(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
(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.
(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
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.
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.