Science Answer the questions.[Phy-2M]

Use of solar cell:

1. To provide electricity in artificial satellites and space probes.
2. To provide electricity to remote areas where normal electricity transmission lines do not exist.
3. To provide electricity to light houses iv. To operate traffic signals, watches, calculators and toys.

Use of wind energy.

1. In the past – in flour mills.
2. At present – for generating the electricity through wind-powered generators.

Einstein’s equation: E=mc² 
where E is the amount of energy produced if mass m is destroyed, and c is the speed of light in vacuum.

Two uses of bio gas:

1. For cooking purpose.
2. For lightning purpose.

Two advantages of biogas:

1. Smoke-free cooking.
2. High calorific value.

Tidal energy is not likely to be a potential source of energy because there are very few sites around the world which are suitable for building tidal barrages, and the rise and fall of seawater during high and low tides is not enough to generate electricity on a large scale.

LPG is considered as good fuel because it has a high calorific value gives a smokeless flame.

LPG is considered as a better fuel than coal because it has a higher calorific value, while burning it does not produce any smoke.

Hydrogen is a cleaner fuel because burning of hydrogen produces only water. which is harmless; but burning of CNG produces CO₂ and water. CO₂ produces greenhouse effect.

Thermal power plant causes serious air pollution because it emits harmful gases and flyash into the air.

Concave and plane mirrors are used for making solar cooker because concave mirror converges a large amount of sun’s rays at a point that is required for high heating and plane mirror reflects the rays of light in the form of a strong beam of sunlight on the top of the box that is required for moderate heating.

Difference between thermal power plant and hydro power plant:

• Thermal power plant uses non-renewable sources of energy like coal, oil or gas; whereas hydro power plant uses renewable source of energy i.e. water.
• Thermal power plant causes pollution due to the burning of fossil fuels; whereas hydro power plant is environment friendly.

Renewable source of energy can be used again and again endlessly, where as non-renewable source of energy cannot be renewed once used.
Ex. Renewable sources of energy are wind energy, ocean energy.
Non-renewable sources of energy are coal, fossil fuel.

The amount of solar energy received per second by one metre square area of the near earth space (exposed perpendicularly to the sun rays) at an average distance between the sun and the earth, is known as solar constant. Its value is 1.4kJ/s/ m².

The traditional sources of energy which are familiar to most people are called conventional source of energy.
Example: Wood, coal etc.

A renewable source of energy is the one which is being produced continuously in nature and is inexhaustible.
Ex. wind energy, ocean thermal energy etc.

The dead parts of plants and trees, and the waste material of animals are called biomass. It is the organic matter which is used as a fuel to produce energy. E.g., wood, agricultural wastes and cow dung.

Biogas is a mixture of gases produced by anaerobic degradation of biomass in the presence of water but in the absence of oxygen. Methane is the major component of biogas.

Nuclear reactor is a device designed to maintain a chain reaction producing a steady flow of neutrons generated by the fission of heavy nuclei. Uranium-235 is used as a fuel in a nuclear reactor.

Pollution caused by the burning of fossil fuels can be controlled by the increasing the efficiency of combustion process and by using various techniques to reduce the escape of harmful gases and ash into the surrounding air.

Advantages of nuclear energy:

1. It produces a large amount of useful energy from a very small amount of a nuclear fuel.
2. Once the nuclear fuel is loaded into the reactor, the nuclear power plant can go on producing electricity for two to three years at a stretch. There is no need of feeding the fuel again and again.
3. It does not produce gases like CO₂ or SO₂.

Advantages of using nuclear fuel: Electricity can be produced for almost two to three years with the same uranium fuel in a nuclear power plant.
Disadvantages of using nuclear fuel: The nuclear wastes produced by the fission of uranium235 during the generation of electricity are radioactive and extremely harmful.

Natural fuels formed deep under the earth from the pre-historic remains of the organisms (like plants and animals) are called fossil fuels.
Example: Coal, petroleum and natural gas.

Petrol is obtained from petroleum, which is a fossil fuel. Fossil fuels were originally made by sun’s energy because it was the sunlight of long ago that made plants and animals grow. So, the energy in petrol originally came from the sun.

A safe and efficient method for the disposal of biowastes and sewage materials is to utilise them for producing biogas. This method is advantageous to us for getting energy and manure without polluting the environment.

Sea-waves energy can be harnessed by by the following ways:

1. By setting up floating generators in the sea which would move up and down with the seawaves and their movement would drive the generators to produce electricity.
2. By letting the sea-waves move up and down inside large tubes so that when the waves move up, the air in the tubes is compressed and this compressed air can then be used to turn a turbine of a generator to produce electricity.

Disadvantage of producing hydroelectricity.

1. Large areas of land are required.
2. Large eco-systems get destroyed.

Disadvantage of geo thermal energy:

1. It is not available everywhere.
2. Deep drilling in the earth is required, which is technically very difficult and expensive.

Advantages of using wind energy for generating electricity:

1. It does not cause any pollution.
2. It is available free of cost.

Advantage of producing hydroelectricity:

1. It does not cause any environmental pollution.
2. It uses the energy of flowing water, which is a renewable source of energy.

Advantage of geothermal energy:

1. It is very economical to use.
2. It does not cause any pollution.

Disadvantages of nuclear energy:

1. The waste products of nuclear fission reactions are radioactive which keep on emitting harmful radiations for thousands of years and are difficult to store or dispose safely.
2. Very high cost of installation is required.
3. There is a limited availability of uranium fuel.

A non-renewable source of energy is defined as the source of energy which has accumulated in nature over a very, very long time and cannot be quickly replaced when exhausted.
Ex. Coal, petroleum etc.

The solar cells convert the energy from sunlight into electrical energy. This electrical energy is converted into chemical energy when the car batteries are charged. When these charged batteries are used, the chemical energy is converted into electrical energy. In the last stage, this electrical energy is converted into kinetic energy for the car by the electric motor that drives the car.

Solar water heater.
Solar cooker.
Solar cell.

Limitations of wind energy:

1. Wind energy farms cannot be established everywhere. They can be established only at those places where wind blows for most part of the year.
2. Wind energy farms require large area of land for their establishment.

The electricity made by the solar cells during day time is stored in rechargeable batteries so that it can be used later on, for example, at night.

In a solar water heater, the storage tank is placed at a higher level than the solar panel containing coils because hot water is lighter and rises up.

1 atomic mass unit = 931 MeV.
25 atomic mass unit = 931 × 25 MeV = 23275 MeV.
23275 MeV of energy is released.

Solar constant is 1.4kW/ m or 1.4kJ/s/ m².
Solar energy received by 1m² area in 1s = 1.4kJ.
Solar energy received by 1m² area in one hour (or 3600s) = 1.4 × 3600 = 5040kJ.

Traditionally, wind energy was used through windmills to pump water from a well and to grind wheat into flour. But the traditional use has been modified and now it is used for the generation of electricity.

Traditionally, the energy of flowing water has been used for rotating the water-wheels and for driving water-mills to grind wheat to make flour. The traditional use of energy of flowing water has been modified by improvements in technology and it is now used to generate electricity.

Natural gas is considered to be a good fuel because it has a high calorific value, burns with a smokeless flame, causes no air pollution and does not produce any poisonous gas.

The fast moving wind strikes the wind turbine which starts rotating. The shaft of the wind turbine also rotates and drives the generator which produces electricity.