PHYSICS [2 Mark Question Answer]

Environmental consequences of using fossil fuels are:
1. Burning of fossil fuel causes air pollution.
2. Burning of fossil fuel can cause acid rain which corrode the buildings, monuments and reduces the fertility of the soil.
3. Smog is caused by burning of fossil fuels which block the sun's radiations and hence hamper the process of photosynthesis.
4. Burning of fossil fuels release green house gases, which in turn be the source of global warming.

Hot spots: The places under the surface of earth, where hot magma collects at fairly less depths, are called hot spots of the earth.
If hot spot does not come in contact with underground water then two holes are made in the earth's crust. Through one hole is pumped in cold water. The cold water on coming in contact with the hot spot changes to super heated steam, which emerges out from the other hole. The steam is then made to run a turbine coupled with generator to produce electricity.

Difference between nuclear fission and nuclear fusion are:
Nuclear fission:
1. In a nuclear fission, a heavy nucleus splits up into lighter nuclei.
2. Harmful radiations are emitted in nuclear fission
3. It starts when slow neutrons bombards the heavy nucleus like ranium-235
4. It causes much pollution.
5. A large amount of energy is released in nuclear fission.
6. It can be controlled.
Nuclera fusion:
1. In a nuclear fusion, two or more light nuclei combine to form a heavy nucleus.
2. No harmful radiations are emitted in nuclear fusion.
3. It starts when light nuclei are heated at very high temperautre.
4. It causes no pollution.
5. Energy released in nuclear fusion is much more than nuclear fission.
6. It can not be controlled.

1. Nuclear fission: The process by which a heavy unstable nucleus (such as w-235) is broken into two medium-weight nuclei by the bombardment of a slow neutron, so as to liberate more neutrons and tremendous amount of energy is called nuclear fission.
2. Nuclear fusion: The process in which two or more light nuclei combine together to form a heavy nucleus along with the release of very large amount of energy is called nuclear fusion.

Charcoal is considered a better fuel than wood because of the
following reasons:
1. Calorific value of charcoal is higher than the calorific value of wood.
2. It produces no smoke.
3. It burns easily without any flame.

Use of cow-dung in biogas is preferred to burning of cow-dung cakes because:
1. Biogas does not produce any smoke and hence causes no pollution.
2. Biogas leaves behind no ash on burning.
3. Calorific value of biogas is very high as compared to cow-dung cakes.
4. Biogas can be used for driving engines of tube wells while cow-dung cakes can not be used for this purpose.

Uses of biogas :
1. It is used for cooking.
2. Its calorific value is very high.
3. It is an eco-friendly source of energy.

Advantage of box type solar cooker :
1. It is used for cooking food.
2. It costs nothing for cooking the food.
3. No loss of nutritions value of ood.
4. It causes no pollution.

Uses of solar energy:
1. Solar energy is used in solar cookers for cooking of food.
2. Solar energy is used by plants to make their food by photosynthesis.
3. Solar energy is used to produce electricity with the help of solar cells.
4. Solar energy is used for providing electricity to electronic calculators and wrist watches.

Limitations of solar energy:
1. This energy can not be used at night.
2. This cannot be used where solar rays are less in power
3. Solar energy produces only d.c. electricity which cannot be used for household purposes.

Renewable sources: Solar energy, wind energy, hydro-energy, geo-thermal energy and nuclear energy.
Non-renewable sources: Coal, petroleum and natural gas.