Page 1 - Sources of Energy

14

CHAPTER
Sources of

Energy

n Class IX, we learnt that the total energy during a physical or chemical
Iprocess is conserved. Why, then, do we hear so much about the energy
crisis? If energy can neither be created nor destroyed, we should have
no worries! We should be able to perform endless activities without
thinking about energy resources!
This riddle can be solved if we recall what else we learnt about energy.
Energy comes in different forms and one form can be converted to another.
For example, if we drop a plate from a height, the potential energy of the
plate is converted mostly to sound energy when it hits the ground. If we
light a candle, the process is highly exothermic so that the chemical
energy in the wax is converted to heat energy and light energy on burning.
What other products are obtained when we burn a candle?
The total energy during a physical or chemical process remains the
same but suppose we consider the burning candle again – can we
somehow put together the heat and light generated along with the products
of the reaction to get back the chemical energy in the form of wax?
Let us consider another example. Suppose we take 100 mL of water
which has a temperature of 348 K (75°C) and leave it in a room where
the temperature is 298 K (25°C). What will happen? Is there any way of
collecting all the heat lost to the environment and making the water hot
once it has cooled down?
In any example that we consider, we will see that energy, in the usable
form, is dissipated to the surroundings in less usable forms. Hence, any
source of energy we use, to do work, is consumed and cannot be used again.

14.1 WHA
14.1 WHAT IS A GOOD SOURCE OF ENERGY?T IS A GOOD SOURCE OF ENERGY?
14.1 WHA
14.1 WHAT IS A GOOD SOURCE OF ENERGY?
14.1 WHAT IS A GOOD SOURCE OF ENERGY?T IS A GOOD SOURCE OF ENERGY?
What can then be considered a good source of energy? We, in our daily
lives, use energy from various sources for doing work. We use diesel to
run our trains. We use electricity to light our street-lamps. Or we use
energy in our muscles to cycle to school.
Activity 14.1
Activity 14.1
Activity 14.1
Activity 14.1
Activity 14.1
 List four forms of energy that you use from morning, when you
wake up, till you reach the school.
 From where do we get these different forms of energy?
 Can we call these ‘sources’ of energy? Why or why not?

242 Science