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Explain the classification of different sources of energy?


Energy sources can be classified as: 

(i) Non-renewable resources: The sources of energy which are produced under special circumstances over millions of years due to slow changes. The process involved is not continuous.
E.g., Fossil fuels like coal, petroleum and natural gas are non-renewable energy sources. With the present rate of their consumption, it is estimated that known deposits of petroleum in our country will be exhausted in another 200 years and that coal may last for another 250 years.

(ii) Renewable sources: The sources of energy which can be harnessed into energy so long as the earth derives its heat and light from the sun are renewable sources. 
E.g., flowing water, wind, tides, ocean waves and biogas are examples of renewable sources. Wood is also a renewable source of energy.

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What are thermal power plants? How will you demonstrate that thermal energy is converted into electrical energy?


Thermal power plants convert heat energy into electrical energy. In thermal power plants, fuels are burnt to heat up water to produce steam which is designed to run the turbine to generate electricity. In the class it can be demonstrated as follows:

Thermal power plants convert heat energy into electrical energy. In t
Fig. Outlines for production of electricity at thermal power plant

Take a tennis ball and make three slits into it. Fit three small fins of a metal sheet into these slits. Fix the tennis ball on an axle as shown so that the ball has a free rotation. Now connect this axle to a bulb through a dynamo. Direct a jet of steam from a pressure cooker on to the fins of the ball. Soon the bulb will start glowing. It will remain glowing till the ball is rotating with the help of steam.
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What are the main constituents of biogas? Describe with a labelled diagram how it is prepared in a fixed dome type plant. What is the advantage of this plant?


Methane is the main constituent of biogas. Other gases present with it are hydrogen, carbon dioxide and hydrogen sulphide. Biogas is prepared in a fixed dome type plant as follows:
Fixed dome type biogas plant: It consists of underground tank T called digester tank which is made of bricks. It has a dome-shaped roof made of cement and bricks. The dome of the digester tank acts as a gas holder. There is a gas outlet through a valve at the top of the

Methane is the main constituent of biogas. Other gases present with i
Fig. Fixed dome type biogas plant

dome. On the left side of the digester tank is a sloping inlet chamber and on the right side is a rectangular outlet chamber, both made of cement and bricks. The inlet chamber is connected to a mixing tank while the outlet tank is connected to the overflow tank.

Working: Cattle dung and water are mixed in equal proportions in the mixing tank M to prepare slurry. The slurry is fed into digester tank T through the inlet chamber I. The tank is filled only up to the cylindrical level so that enough space is available for the biogas that would be formed. The tank is closed for 50 to 60 days. During this period animal wastes etc. undergo fermentation by anaerobic microorganisms in the presence of water. Gases such as methane, carbon dioxide, hydrogen, hydrogen sulphide etc. (biogas) start collecting in the dome. As more and more biogas collects in the dome, it exerts pressure on the slurry in the digester tank and forces it to go into the overflow tank F through the outlet chamber. The biogas collected can be used through the outlet valve at the top of the dome. The spent slurry obtained in the overflow tank can be used as manure as that is rich in nitrogen and phosphorus compounds.
Once the biogas plant becomes operative, more and more slurry may be fed into it to give a continuous supply of biogas.
Instead of animal dung, domestic sewage or human excreta may also be used in the biogas plant. The above fixed dome type plant is cheap, easy to construct and is also called Janta gobar gas plant.
The main advantage of fixed dome type plant is that it cannot be corroded and thus used over the years whereas the gas holder used in floating dome is made of steel and is corroded over the time and needs replacement.

 

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What is windmill? Draw a diagram to show how a windmill can be used to draw water from the ground.

Windmill is a simple device which works with the energy of the flowing wind. Huge blades are mounted on a suitable support in a wheel type arrangement so that these are rotated with the moving wind.


Windmill is a simple device which works with the energy of the flowin
Fig. Windmill used to lift water from flooded mines

The number of blades, their shape and the height of the windmill from the ground are decided on the basis of wind velocity and other environmental factors. The blades of a windmill are designed to create a pressure between its different regions when wind strikes them. This difference in pressure makes the blades to rotate.

These blades are connected to a long rod having a U shaped bend at the other end. The U shaped bend of the crank is connected to the rod of water pump. During the moving wind, as the wheels are rotated, the crank rod moves up and down and simultaneously the rod of water pump also moves up and down. The up and down motion of the pump rod would lift the water from ground.

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What causes the wind to blow? Explain the principle of working of a windmill. State two advantages of using wind energy.

Wind and air movement is generated as a result of unequal heating of the landmass and water bodies by solar radiation. The kinetic energy associated with the movement of large masses of air is the wind energy. This kinetic energy was harnessed by wind mills in the past to do mechanical work.
Kinetic energy can be used to do work. This work is used to power windmills, sail boats and gliders.

Principle of working windmill: The blades of a windmill are designed in such a way that when wind blows over them, a pressure difference is created over different regions. This pressure difference rotates the blades. To produce electricity, the rotatory motion of blades is utilized to rotate the turbine of the electric generator.
In a water lifting machine, the rotatory motion of the blades is made to do mechanical work.

Advantages of using wind energy:
(i) It does not cause pollution in the environment.
(ii) The cost of using fuel (i.e., air) is nil. 
 
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