Cbse science activity 14.3 ncert
Answers
CHAPTER14
I
n Class IX, we learnt that the total energy during a physical or chemical
process 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 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
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?
Sources of Energy 243
The muscular energy for carrying out physical work, electrical energy
for running various appliances, chemical energy for cooking food or
running a vehicle all come from some source. We need to know how do
we select the source needed for obtaining the energy in its usable form.
Activity 14.2
Consider the various options we have when we choose a fuel for
cooking our food.
What are the criteria you would consider when trying to categorise
something as a good fuel?
Would your choice be different if you lived
(a) in a forest?
(b) in a remote mountain village or small island?
(c) in New Delhi?
(d) lived five centuries ago?
How are the factors different in each case?
After going through the two activities above, we can see that the
particular source of energy, or fuel, we select for performing some work
depends on many different factors. For example, while selecting a fuel,
we would ask ourselves the following questions.
(i) How much heat does it release on burning?
(ii) Does it produce a lot of smoke?
(iii) Is it easily available?
Can you think of three more relevant questions to ask about a fuel?
Given the range of fuels we have today, what are the factors which
would limit our choices when it comes to a particular task like cooking
our food? Would the fuel selected also depend on the work to be done?
For example, would we choose one fuel for cooking and another for
heating the room in winter?
We could then say that a good source of energy would be one
which would do a large amount of work per unit volume or mass,
be easily accessible,
be easy to store and transport, and
perhaps most importantly, be economical.
QUESTIONS
? 1. What is a good source of energy?
2. What is a good fuel?
3. If you could use any source of energy for heating your food, which one
would you use and why?
Answer:
Activity 14.3 NCERT Class 10 Science Sources of Energy
OBSERVATION:
The pressure of steam from a pressure cooker rotates the turbine. It rotates the dynamo, and the bulb starts glowing.
EXPLANATION:
A dynamo has numerous wire coiled around a strong magnet. Movement in these wires produces electricity by electromagnetic induction. As a result, electricity is produced which glows the bulb.
APPLICATION:
A thermal power plant and a hydroelectric plant works on the same principle. In a thermal power plant, the energy of coal produces steam, and steam rotates the turbine. In a hydroelectric plant, Energy of flowing water rotates the turbine.