# Work, Energy, and Power

## ðŸ‘‰Â All Chapter ContentsÂ ðŸ‘ˆÂ

• 4.2 Energy

• 4.3 Different Forms of Energy

• 4.4 Sources of Energy

• 4.5 Conservation and Transformation of Energy

• 4.6 Relation between mass and Energy

• 4.7 Power

What is a transformation of energy?

Energy changes from one state to another. This change is called the transformation of energy.

What is a watt?

If one-joule work is done in one second or the rate of transformation of energy is called a watt.

Write down the dimension of energy.

The dimension of energy is [E] = [ML2T-2]

How many types of energy exist?

There are various types of energy. We are more or less familiar with nine (9) types of energy.

Define the unit of work.

The SI unit of work is the joule. If a force of 1 N is applied on an object and it moves 1 m along the direction of the force then the work done is said to be 1 joule.

What is mechanical energy?

The energy produced by a machine is called mechanical energy. The ability of a body to do mechanical work is called mechanical energy.

Write down the principle of conservation of energy?

Energy cannot be created, neither be destroyed, it can transform from one form to another or multiple forms. The total amount of energy of the universe is constant and unchangeable.

What kind of quantity is work?

Work is a scalar quantity.

What kind of quantity is energy?

Energy is a scalar quantity.

What is the unit of energy?

The unit of energy is joule (J).

What is the unit of work?

The unit of work is joule (J).

What is work?

If force can displace a body from its original position then it is called work. So, work = Force x Distance along the applied force.

What are the common sources of energy?

Coal, mineral Oil and natural gas are the common sources of energy.

What kind of substance is coal?

Coal is an organic matter.

What can be found from coal?

Coal gas, mineral oil and natural gas are the common sources of energy.

What is needed to run steam engine?

Coal is needed to run steam engine.

What is the main material of heat electric plant?

The main raw material of heat is coal.

What emits while coal is burnt?

Sulphur smog emits when coal is burnt.

What is the cause of acid rain?

The burning of coal emits sulphur smog which causes acid rain.

What can be found from petroleum?

Petrol, pitch that is used to pave roads, kerosene, chemical fertilizer, etc. are all petroleum products.

From which language did the word 'petroleum' come?

Petroleum is a Latin word.

Which words make up the word 'Petroleum'?

Petroleum is a combination of 'Petro' and 'Olium'.

What is the meaning of 'Petroleum'?

Petroleum means oil of stones, i.e oil stored inside stone.

Write down three sources of non-renewable energy?

Three sources of non-renewable energy are - Coal, Mineral oil and Natural gas.

What is renewable energy?

The energy that can be reproduced or replenished again and again is called renewable energy.

Write down three sources of renewable energy?

The three sources of renewable energy are- i) Solar energy, ii) Wind energy & iii) Biogas.

Give two examples of solar energy?

Two examples of solar energy are-

i) Solar water heater & ii) Solar cooker.

What is Nuclear energy?

If a heavy atom is hitted with neutron, massive amount of energy is released. This energy is called nuclear energy.

What is meant by kinetic energy of 500 J of a body?

Kinetic energy of 500 J of a body means-

i) If the body moves at a certain velocity, because of motion it can do 500 J of work.

ii) If force is applied to stop the body, the body will work an amount of 500 against the applied force until the body stops.

Differentiate between work and power.

The differences between work and power are-

1) Work is denoted by 'w' and Power is denoted by 'P'.

2) The unit of work is joule (J) and The unit of power is watt (W).

3) The dimension of work is [ML2T-2] and The dimension of power is [ML2T-3].

4) Time is not needed to measure work and Time is essential to measure power.

What is meant by one horse power?

Horse Power is a unit of power. This unit of power was used earlier. Still today this unit is sometimes used to mean the power of a motor or a car.

What is efficiency?

Efficiency means the ratio of effective energy and the total given energy. Usually efficiency is expressed in percentage.

The efficiency of an engine is 90%? What is meant by this?

The efficiency of an engine is 90% means, if 100 unit of energy is given to that engine the amount of work done will be 90 unit.

What is the meaning of 60 W's electric bulb?

The meaning of 60 W's electric bulb -

i) The amount of electricity needed to light the bulb can do 60 J of work per second.

ii) The electric power of the bulb is 60 watt.

All moving objects are in possession of kinetic energy - explain.

Creating velocity in a body in rest or increasing the velocity of a moving object means to produce acceleration in it. For this, force has to be applied. As a result work will be done on the body. For this the body will obtain the ability to work and this work will be stored in the object as kinetic energy. This is why all moving objects are in procession of kinetic energy.

Potential energy depends on the height of the body. - explain.

If a body of mass m is raised to a height h above the surface of the earth, the work doen in such a process is a measure of potential energy stored in the body. We know, potential energy = weight of the body x heightÂ

Ep = mgh

So, from the equation we can see that potential energy depends on the vertical height of the object from any surface. The more is the height, the higher will be the potential energy. So, we can say that, "Potential energy depends on the height of the body.

What is meant by 1 watt?

If one joule work is done in one second or the rate of transformation of energy is called one watt.

What is meant by an electric power station having a power of 200 MW?

200 MW power of an electrical power station means that it supplies 200000000 joules of energy in one second.

## Question Bank

• What is work?
• What is the unit of work?
• What is the dimension of work?
• What do you understand by 40 J work?
• What is one Joule?
• What is positive work?
• What is negative work?

## 4.2 Energy

• What is energy?
• What is the unit of energy?
• What is the dimension of energy?

• Write the names of the different forms of energy.
• What is kinetic energy?
• What is potential energy?
• What does the potential energy depend on?
• What do you mean by 300 J of the potential energy of an object?
• What do you mean by 300 J of the kinetic energy of an object?

## 4.4 Sources of Energy

• What do you mean by chemical energy?
• Describe the different types of chemical energy.
• Describe the contribution of coal considering its economic, social, and environmental impact.
• Describe the contribution of natural gas considering its economic, social, and environmental impact.
• What do you mean by solar energy?
• Write the use of solar energy.
• What is hydroelectricity?
• How can hydroelectricity be generated?
• What is wind energy?
• Write the uses of wind energy.
• What do you understand about geothermal energy?
• Write the impact of energy transformation on the environment.

• What is the conservation of energy?
• What do you understand by the transformation of energy?
• How electrical energy is transformed?
• How chemical energy is transformed?
• How heat energy is transformed?
• How mechanical energy is transformed?
• How light energy is transformed?

## 4.6 Relation between mass and Energy

• Explain the meaning of the equation E = mc2.
• 1 eV = How many Joules?
• 200 MeV = How many Joules?
• 1-kilowatt hour = How many Joules?
• What is the nuclear reaction?
• What is a chain reaction?

• What is power?
• What is the unit of power?
• What is the dimension of power?
• What do you mean by one watt?
• What does 40 W mean on an electric bulb?
• Write the differences between work and power.
• Write the differences between energy and power.

## 4.8 Efficiency

• What is efficiency?
• Why can't be the efficiency of an instrument 100%?
• What do you understand by the efficiency of an instrument being 80%?

• Explain the role of energy in development activities.

No Comment