Page 68 - Science Class 08

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i Substance which is burnt to obtain heat at reasonable cost is called fuel.
i Calorific value of a fuel is the amount of heat produced when one gram of the fuel is burnt
completely in a sufficient supply of air. It is expressed in J/g or kJ/g.
i The minimum temperature at which a substance catches fire and starts burning is called its
ignition temperature.
i A good fuel has low ignition temperature and high calorific value.

i Fuels can be solid, liquid or gaseous.
i The sources of energy can be categorised into exhaustible sources and inexhaustible sources.
i Coal, petrol, natural gas, etc. are exhaustible sources of energy.

i Anthracite, Bituminous coal and lignite are different types of coals having carbon in
different amounts.
i Different products of coal are obtained by destructive distillation of coal.
i Coke, coal gas, coal tar, water gas, producer gas, etc. are different products of coal.

i The process of heating coal in the absence of air is called destructive distillation of coal.
i Natural gas is less polluting. That’s why it is also called clean fuel.

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A. Tick (3) the correct op on.
1. Which of the following fuels has maximum calorific value?
(a) Kerosene (b) Coal
(c) Petrol (d) Methane
2. Which of the following is an exhaus ble natural resource of energy?

(a) Air (b) Water
(c) Soil (d) All of these
3. Which of the following is not a primary fuel?

(a) Coal (b) Wood
(c) Natural gas (d) Coke
4. Inexhaus ble natural resources are known as:
(a) limited (b) unlimited

(c) scarce (d) both (a) & (b)
5. Which of the following states does not produce petroleum?
(a) Assam (b) Gujarat

(c) Maharashtra (d) Mumbai
6. Which of the following is the best quality of coal?
(a) Anthracite (b) Bituminous
(c) Lignite (d) Petrol

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