Page 60 - Science Class 08
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harmful gases and smoke cause pollu on and effects on environment like acid rain, global
hence these fuels are generally avoided. warming, air pollu on, etc. But, natural gas does
Coal and petroleum cause pollu on. They not cause pollu on. It is, therefore, the
release harmful and poisonous gases and popularity of natural gas is increasing day-by-
oxides which do not only cause severe disease day. In many big ci es, public transports are
to human beings, but also cause harmful powered by CNG (Compressed Natural Gas).
1. What is the need for fuel?
2. How calorific value of a fuel is found?
3. Wood has lower igni on point than coal. Does it mean wood is be er fuel than coal?
4. Why the transporta on of petroleum is easier than that of coal?
SOURCE OF ENERGY
Exhaus ble Sources Inexhaus ble Sources
Fossil Fules Solar Wind Water Tidal Geothermal
Energy Energy Energy Energy Energy
Coal Petroleum Natural Gas
Exhaus ble Sources of energy is that they do not cause any kind of
pollu on. But, the exploita on of these sources
There are some energy sources which can be
used only once. These energy sources are of energy is not very much easy. We s ll lack
suitable technique for their exploita on.
called exhaus ble sources of energy.
TYPES OF FUELS
For example, coal, petrol, natural gas, etc. We
cannot use these resources again and again. You already know about various types of fuels.
These exhaus ble sources are also called fossil Now, you will study about the classifica on of
fuels because they are made of dead plants fuels. Fuels can be classified in number of ways.
and animals. We will discuss about the fossil However, we classify them on the following
fuels later in this chapter. basis:
Inexhaus ble Sources v Physical State v Occurrence
There are some energy sources which can be Physical State
used again and again and they cannot be Fuels are obtained in all the three physical
exhausted. These energy sources are, therefore, states— solid, liquid and gas.
called inexhaus ble sources of energy. These
Solid : Some fuels are obtained in solid state
sources of energy are in a great abundance.
like wood, coal, ca le dung cakes, biogas (the
For example, solar energy, wind energy, moving remains of sugarcane a er the extrac on of
water energy, dal energy, geothermal energy. juice), charcoal, wax parafin, etc.
The most important advantage of these sources
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