# Various Forms Of Energy Class-7th Goyal Brothers Physics Solutions Ch-3 Unit-2

Various Forms Of Energy Class-7th Goyal Brothers Physics Solutions Chapter-3. We Provide Step by Step Answers of Objective, True False , Fill in the blanks, Match the following , Study Questions of Chapter-3 Energy , Unit-2(Various Forms Of Energy and their interconversion) Visit official Website  for detail information about ICSE Board Class-7.

## Various Forms Of Energy Class-7th Goyal Brothers

Physics Solutions Ch-3 (unit-2)

 Board ICSE Class 7th Subject Physics Book Name Goyal Brothers Theme-3 Energy Unit-2 Various Forms Of Energy and their interconversion Topic Solution of exercise questions Session 2023-24

### OBJECTIVE TYPE QUESTIONS

#### A. Fill in the blanks :

1. A loudspeaker converts electric energy into _sound_ energy.
2. During digestion of food the chemical energy of food changes into _heat_ energy.
3. During photosynthesis, the ight energy changes into _chemical_ energy.
4. _Nuclear_ energy is released in the form of heat energy when an atom splits.
5. In hydroelectric dams, the kinetic energy of flowing water is transformed into _electric_ energy.

#### B. Write ‘True’ or ‘False’ for the following statements :

1. In wind power stations the kinetic energy of wind changes into electric energy. [T]
2. The source of energy in atom bomb is its chemical energy. [F]
3. An electric bulb converts electric energy into light energy only. [T]
4. The energy in an electric cell is stored in the form of chemical energy. [T]
5. Magnetic energy always causes repulsion. [F]

#### C. Statement given below are incorrect. write the correct correct statement:

1. The energy released during splitting of nucleus of an atom is in the form of light energy.

Correct Statement: The energy released during splitting of nucleus of an atom is in the form of nuclear energy.

2. When an electric current flows through an electric bulb, the electric energy first changes to light energy and then to heat energy.

Correct Statement: When an electric current flows through an electric bulb, the electric energy first changes to heat energy and then to light energy.

3. When we speak in front of a microphone, the light energy changes into electric energy.

Correct Statement: When we speak in front of a microphone, the sound energy changes into electric energy.

4. During the charging of a inverter battery, the chemical energy changes into electric energy.

Correct Statement: During the charging of a inverter battery, the electric energy changes into chemical energy.

5. During photosynthesis by plants, the heat energy changes to light energy.

Correct Statement: During photosynthesis by plants, the liquid energy changes to chemical energy.

#### 1. Light of a bulb is an example of conversion of :

(a) heat energy into light energy

(b) electric energy into heat energy

(c) electric energy into light energy

(d) Both (b) and (c)

Ans: (d) Both (b) and (c)

#### 2. A vibrating body possesses :

(a) sound energy

(b) light energy

(c) electric energy

(d) magnetic energy

Ans: (a) sound energy

#### 3. Energy is neither created nor destroyed in a system, is known as :

(a) law of conservation of mass

(b) law of conversion of mass

(c) law of conservation of energy

(d) law of conversion of energy

Ans: (c) law of conservation of energy

#### 4. Flowing water turns the blade of turbine because it possesses:

(a) potential energy

(b) kinetic energy

(c) Both (a)  and (b)

(d) none of these

Ans: (a) potential energy

#### 5. When we wind a watch, the muscular energy changes into :

(a) sound energy

(b) magnetic energy

(c) kinetic energy

(d) potential energy

Ans: (d) potential energy

#### 5. photo-voltaic cell

 Column A Column B 1. A device which converts electric energy into heat and light energy. 4. electric bulb 2. A device which converts electric energy into sound energy. 3. loud  speaker 3. A device which converts electric energy into magnetic energy. 1. Electromagnet 4. A device which converts light energy into electric energy. 5. photo-voltaic cell 5. A device which converts electric energy into mechanical energy. 2. Electric motor

STUDY QUESTIONS

#### (b) Explain potential energy by giving an example.

(a) Potential energy refers to the energy which an object holds due to its position relative to other objects, stresses within itself, its electric charge, or other factors.

(b) For example- Potential energy possessed by water is used to harness electrical energy. Water raised to a certain height gains potential energy with respect to the ground due to the gravitational force acting on it.

#### (b) Explain kinetic energy by giving an example.

(a) Kinetic energy is the energy an object has because of its motion. If we want to accelerate an object, then we must apply a force. Applying a force requires us to do work. After work has been done, energy has been transferred to the object, and the object will be moving with a new constant speed

(b) A river flowing at a certain speed comprises kinetic energy as water has a certain velocity and mass.

#### (b) By giving an example, prove that heat is a form of energy which is capable of doing work.

(a) The energy released when we burn wood, coal, oil or gas is called heat energy. Steam possesses the heat energy which is capable of doing work. Therefore we can say that heat is a form of energy which is capable of doing work

(b)  The water in the pressure cooker is converted into steam by the heat energy in the burning flame under the pressure cooker. The water and the steam get energy from the heat. This energy works by displacing the nozzle. So, we can say heat is a form of energy.

#### Question 4. By giving an example describe:

(a) Light energy: Light energy is a kind of kinetic energy capable of allowing various forms of lights visible to the human eyes. Light is known as a type of electromagnetic radiation produced by hot objects such as lasers, bulbs and sunlight.

A light bulb, the glowing tubes in a toaster, the sun, and even automobile headlights are examples of light energy.

(b) Electric energy: is the energy (both kinetic and potential) in the charged particles of an atom that can be used to apply force and/or do work. That means that electrical energy has the capacity to move an object or cause an action.

Lightning, during a thunderstorm, is an example of electrical energy.

(c) Magnetic energy: A magnet is capable of causing motion in the magnetic substances, it has an energy which may be called magnetic energy.

Example- Magnetic energy is used in electromagnets fixed in the cranes to lift heavy loads of iron or separate iron scrap from the heap of waste material

(d) Chemical energy:  It is the energy that is stored in the bonds of chemical compounds such as atoms and molecules. Chemical energy is released when a substance undergoes a chemical reaction and produces heat mostly in the form of a by-product.

Examples of stored chemical energy are biomass, batteries, natural gas, petroleum, and coal.

(e) Nuclear energy: Nuclear energy is a form of energy released from the nucleus, the core of atoms, made up of protons and neutrons.

Medical Diagnosis and Treatment are the examples of nuclear energy.

#### Question 5. Name a device which changes

(a) Chemical energy into light energy – Voltaic cell

(b) Electric energy into heat energy – Electric bulb

(c) Heat energy into Electric energy – Electric generator.

(d) Electric energy into magnetic energy – Electromagnet

(e) Electric energy into light energy – Electric bulb

(f) light energy into electric energy – Photo-voltaic cell

(g) Electric energy into sound energy – Loudspeaker

(h) light energy into chemical energy – Photosynthesis

#### Question 6. Describe how sun is the ultimate source of energy .

Answers: The sun is called the ultimate source of energy because it is the source of almost all energies of the earth. Plants convert light energy from the sun into chemical energy (food) by the process of photosynthesis.

#### (c) Show that the sum of potential energy and kinetic energy remains the same by giving the example of roller coaster car.

(a) The law of conservation of energy states that the amount of energy is neither created nor destroyed. For example, when you roll a toy car down a ramp and it hits a wall, the energy is transferred from kinetic energy to potential energy.

(b) Energy can neither be created nor destroyed. It can only be transformed from one to another is the law of conservation of energy. For example , object falling from certain height converts its potential energy to kinetic energy and at all instant total mechanical energy remains constant.

(c) A roller coaster operates on the law of conservation of energy. Initially, some work is done to put the roller coaster car at the top position. This work done is stored in the roller coaster car in the form of potential energy. But it’s kinetic energy is zero due to its stationary position.

— : end of Various Forms Of Energy Class-7th Goyal Brothers Physics Solutions Chapter-3 Unit-2 :–-