Very Short Answer Type Questions
Q.1. What is meant by calorific value of a fuel ? 
Ans. The amount of heat obtained on burning units mass of a fuel is called its calorific value.

Q.2. On what principle does solar heater work ? 
Ans. Solar heater works on the principle of solar heating devices.

Q.3 Write full name of L.P.G. and C.N.G.
Ans. L.P.G.- Liquified Petroleum Gas, C.N.G.- Compressed Natural Gas.

Q.4. Name the renewable source of energy.
Ans. Wind energy, Solar energy, Biogas etc.

Q.4. Name the non renewable source of energy.
Ans. Coal, natural gas, petroleum etc.

Short Answer Type Questions
Q.1. Natural gas is considered to be a good fuel. Why ?(mp 2011, 15, 17)
Ans. The natural gas is considered to be a good fuel because :
(i) it has calorific value.
(ii) it is pollution free.
(iii) it is easy to store and transport.
(iv) It does not produce smoke on burning.
(V) it does not produce any harmful residue on burning .

Q.2. What do you understand by chain reaction ?
Ans. Chain Reaction : When U235 atom is bombarded with a neutron, it gets fissioned to produce two light nuclei and huge amount of energy is released along with three neutrons. These 3 neutrons in turn, cause the fission of other uranium atoms and this way the reaction multiplies. This multiple reaction is called chain reaction.

Q.2. Write the effects of energy crisis on human society
Ans. The effects of energy crisis created by increasing population and that of consumption of energy on human society will be the following :(i) it will be very difficult to cook the food.
(ii) Means of transportation will be useless.
(iii) industrial development will be stop.
(iv) Life style will be damaged.

Q.4. Due to combustion of petroleum, pollution is produced. Why ?
Ans. During combustion of petroleum, pollution is produced because:
Petroleum products are mixture of several hydrocarbons, which on burning give CO2 on complete oxidation and carbon-monoxide (CO) and partial oxidation.

Q.5. Explain how is nuclear radiation harmful to mankind.
Ans. The nuclear radiation is very harmful to mankind in the following ways:
(i) Nuclear radiation pollutes air which cause Lung's cancer.
(ii) Nuclear radiation destroys chromosomes in the cells. (iii) Nuclear radiation pollutes water which cause the death of aquatic life.
(iv) Nuclear radiation creates mutation which cause skin cancer and blood cancer.

Q.6. Biogas plant is boon to farmers. Why ?
Ans. Biogas plant is considered to be a boon to farmers because the raw materials like animal dung, agriculture wastes etc are easily available to farmers. The wastes (Residues ) obtained by a biogas plant is used as manure and fertilizers. Biogas is used to fulfill their today energy requirement.