PhysicsICSE Class 10 · Different Types of Energy

Energy Conversions: Forms of Energy, Device Chains and Solved Questions (ICSE Class 10)

Updated 15 October 2026 · Fact-checked

Energy can change from one form to another but is never created or destroyed. The main forms are mechanical (potential and kinetic), chemical, heat, light, sound, electrical and nuclear. A burning candle changes chemical energy into heat and light; a motor changes electrical energy into mechanical energy, with some heat and sound.

Name each conversion by its input and outputs: candle chemical to heat and light, motor electrical to kinetic and heat, dynamo mechanical to electrical.

Illustration drawn for QuestionBuddy.

Understand Energy Conversions: Forms of Energy and Examples

Forms of energy (named in the syllabus):

Mechanical energy: potential energy (position or shape) plus kinetic energy (motion).
Chemical energy: stored in the bonds of substances, released in reactions. Fuels, food, cells and batteries store it.
Heat energy: the energy of the random motion of particles; flows from hot to cold.
Light energy: carried by light; it lets us see and drives photosynthesis and solar cells.
Sound energy: carried by vibrations through a medium.
Electrical energy: carried by moving charges in a circuit.
Nuclear energy: stored in the nucleus, released in fission and fusion.

Conversion. Every device or natural process changes energy from one form to another. To name a conversion correctly, ask two questions:
1. Where does the energy come from? (the input: what is used up or runs down)
2. What does it become? (the useful outputs, and usually some heat and sound)

The input is the source that keeps the process going, not what started it. A candle is lit by a match, but the energy comes from the wax: chemical → heat + light. A cycle bell is struck by a lever moved by your thumb: kinetic (mechanical) → sound, not 'potential → sound' just because the bell is at a height.

Common examples.

Electric fan, motor: electrical → mechanical (kinetic) + heat + sound.
Generator, dynamo: mechanical → electrical.
Electric heater, iron: electrical → heat. Bulb: electrical → light + heat.
Cell or battery (in use): chemical → electrical. Charging a battery: electrical → chemical.
Loudspeaker: electrical → sound. Microphone: sound → electrical.
Solar cell: light → electrical. Photosynthesis: light → chemical.
Burning fuel: chemical → heat + light. Steam engine: heat → mechanical.
Falling water at a dam: potential → kinetic → (turbine, generator) electrical.
Nuclear reactor: nuclear → heat → mechanical → electrical.

Chains. Many devices are chains: in a thermal power station, chemical energy of coal → heat (furnace) → kinetic energy of steam → rotational KE of the turbine → electrical energy (generator).

Not all output is useful. In every real conversion some energy becomes heat (and often sound) that is not wanted. The energy is not destroyed; it spreads into the surroundings. The fraction that is useful can be found by energy bookkeeping: input $=$ useful output $+$ wasted energy. This leads to the principle of conservation of energy (Chapter 6).

Energy Conversions: Forms of Energy and Examples: formulas and key facts

Energy bookkeeping: $E_{input} = E_{useful} + E_{wasted}$; No energy is created or destroyed.
Useful fraction: $useful % = \frac{E _{useful}}{E _{input}} \times 100$; Always less than 100% in real devices.
Energy from power: $E = P \times t$; Joules from watts and seconds; kW h from kW and hours.

How to solve Energy Conversions: Forms of Energy and Examples questions

Name the input form, then the useful output, then the waste.

1Identify the energy source that is being used up (fuel, battery, food, mains, falling water).
2Identify the useful output (motion, light, sound, heat, electricity).
3Write 'input → output', adding '+ heat' or '+ sound' where some is wasted.
4For a chain, list each stage in order with an arrow.
5For numbers, use input = useful + wasted, and $E = P t$ where power is given.

Energy Conversions: Forms of Energy and Examples in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

One input, several outputs

Suppose you switch on a hair dryer.

List the energy conversions taking place.

Try it first, then show the solutionSolution

Input: electrical energy from the mains.
Outputs: heat (in the heating coil), kinetic energy (the fan that blows the air), and some sound.

Answer: Electrical → heat + kinetic + sound.

Memory hook: Count the outputs you can feel, see and hear.

Mechanical work becomes heat

Imagine rubbing your palms together quickly on a cold morning.

What energy conversion takes place, and where did the energy come from originally?

Try it first, then show the solutionSolution

Your muscles move your hands: the chemical energy of food becomes kinetic energy.
Friction between the palms turns the kinetic energy into heat.

Answer: Chemical (food) → kinetic → heat.

Memory hook: Friction is the toll booth where motion pays in heat.

Tricks to remember Energy Conversions: Forms of Energy and Examples

Short memory aids. Say each one aloud once, then use it on a question the same day.

Source, not starter
The input is what runs down, not what switched it on. A candle's wax, not the match.
Use it when: Candle-type MCQs like 2025 Q1(iii).
Motor in, generator out
Motor: electricity in, motion out. Generator: motion in, electricity out.
Use it when: Device conversion pairs.
Mic and speaker are mirror twins
Microphone: sound → electrical. Loudspeaker: electrical → sound.
Use it when: Sound devices.
Heat always sneaks out
Add '+ heat' to almost every real conversion.
Use it when: Complete answers in 2-3 mark questions.

Energy Conversions: Forms of Energy and Examples: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: An electric fan · 1 mark · MCQBoard level

The main energy conversion in an electric fan is:
(a) mechanical to electrical
(b) electrical to mechanical
(c) heat to electrical
(d) chemical to mechanical

Try it first, then show the solutionSolution

The fan takes electrical energy from the mains.
Its motor turns the blades: kinetic (mechanical) energy, with some heat and sound.

Answer: (b)

Example 2: Two devices · 2 marks · Short answerBoard level

State the energy conversion in (a) a loudspeaker, (b) a storage battery while it is being charged.

Try it first, then show the solutionSolution

(a) Electrical energy → sound energy. (1)
(b) Electrical energy → chemical energy (stored in the cell). (1)

Answer: (a) Electrical → sound (b) Electrical → chemical

Example 3: Chain in a thermal power station · 3 marks · Short answerHarder board level

Write the chain of energy conversions in a coal-fired power station, naming the part where each change happens.

Try it first, then show the solutionSolution

Furnace: chemical energy of coal → heat energy. (1)
Boiler and turbine: heat → kinetic energy of steam → rotational kinetic energy of the turbine. (1)
Generator: mechanical (rotational) energy → electrical energy. (1)

Answer: Chemical → heat → KE of steam → rotational KE → electrical.

Example 4: Where did the rest go? · 3 marks · Short answerHarder board level

An electric motor takes 2000 J of electrical energy and uses it to lift a 15 kg load through 10 m. ( $g = 10 m s^{- 2}$ )
(a) Find the useful energy output.
(b) How much energy is not usefully converted, and into what forms?
(c) What percentage is useful?

Try it first, then show the solutionSolution

(a) Useful (PE gained) $= m g h = 15 \times 10 \times 10 = 1500$ J. (1)
(b) $2000 - 1500 = 500$ J, mainly heat in the motor windings and some sound. (1)
(c) $\frac{1500}{2000} \times 100 = 75%$ . (1)

Answer: (a) 1500 J (b) 500 J, as heat and sound (c) 75%

Example 5: A wind-up toy car · 3 marks · Short answerHOTS / competency

A child winds the key of a toy car, puts it down, and it runs across the floor, slows and stops. Write the full chain of energy conversions, starting from the child's food, and say what finally happens to the energy.

Try it first, then show the solutionSolution

Chemical energy (food, in muscles) → kinetic energy of the hand turning the key. (1)
→ elastic potential energy stored in the wound spring → kinetic energy of the car. (1)
→ heat (friction) and sound as it slows; finally all of it is heat in the floor, car and air. (1)

Answer: Chemical → kinetic → elastic PE → kinetic → heat + sound.

Example 6: Case study: a solar lamp · 4 marks · Case-basedHOTS / competency

Suppose a solar panel on a roof charges a battery during the day, and the battery runs a 20 W LED lamp at night. On a sunny day the panel delivers 100 W for 5 hours, and the battery stores 80% of that.
(a) Write the chain of conversions from sunlight to the lamp's light.
(b) Find the energy delivered by the panel in kW h.
(c) Find the energy stored in the battery.
(d) For how many hours can the lamp run on it?

Try it first, then show the solutionSolution

(a) Light → electrical (panel) → chemical (battery charging) → electrical (battery in use) → light + heat (lamp). (1)
(b) $0.1 kW \times 5 h = 0.5$ kW h. (1)
(c) $0.8 \times 0.5 = 0.4$ kW h. (1)
(d) $\frac{0.4 kW h}{0.02 kW} = 20$ h. (1)

Answer: (a) Light → electrical → chemical → electrical → light + heat (b) 0.5 kW h (c) 0.4 kW h (d) 20 h

Where students lose marks in Energy Conversions: Forms of Energy and Examples

The slips examiners see most often, and what to write instead.

Mistake: Giving a conversion by rote from a similar device
A cycle bell is struck by a lever moved by your thumb, not powered by electricity like a doorbell, and not by its height.
Wrong working
Cycle bell: electrical → sound, or gravitational PE → sound.
Right working
Cycle bell: kinetic (mechanical) → sound.
Do this: Ask where the energy for this particular device comes from.
Usually costs: Reported for 2024 Q1(i).
Mistake: Taking the starter as the input
The match only lights the candle; the wax supplies the energy.
Wrong working
Burning candle: heat → chemical + light.
Right working
Burning candle: chemical → heat + light.
Do this: The input is what gets used up.
Usually costs: Reported for 2025 Q1(iii).
Mistake: Leaving out the wasted heat
A complete answer for a motor or bulb includes the heat produced.
Wrong working
Bulb: electrical → light.
Right working
Bulb: electrical → light + heat.
Do this: Add '+ heat' unless the question asks only for the main conversion.
Usually costs: Half marks in 2-mark answers.
Mistake: Reversing a device pair
Motors and generators, microphones and loudspeakers do opposite conversions.
Wrong working
Generator: electrical → mechanical.
Right working
Generator: mechanical → electrical.
Do this: Generator generates electricity: electrical is the output.
Usually costs: MCQ marks.

Exam tips

The 2024 and 2025 papers each set a 1-mark MCQ on an energy conversion (a cycle bell; a burning candle). Read what powers the device before choosing.
Write conversions with arrows: 'chemical → heat + light'.
For chains, name the part of the device at each step (furnace, turbine, generator).
Qualitative questions on electrical, chemical, heat, nuclear, light and sound energy are in the syllabus; numericals are on K and U only.

Practice questions on Energy Conversions: Forms of Energy and Examples

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The energy conversion in a dry cell supplying current is:
(a) electrical to chemical
(b) chemical to electrical
(c) heat to electrical
(d) light to electrical
Hint
What runs down in a cell?
Answer
(b)
Q2 · 2 marks · Very short answerBoard level
Name a device that converts (a) heat energy into mechanical energy, (b) electrical energy into light energy.
Hint
Think of engines and lamps.
Answer
(a) A steam engine (or any heat engine). (b) An electric bulb (or LED).
Q3 · 2 marks · Short answerHarder board level
Write the chain of energy conversions in a nuclear power station.
Hint
It is like a thermal station with a different heat source.
Answer
Nuclear energy → heat → kinetic energy of steam → rotational KE of turbine → electrical energy.
Q4 · 2 marks · Short answerHarder board level
A 0.2 kg ball dropped from 5 m rebounds to 3.2 m. How much mechanical energy has been converted, and into which forms? ( $g = 10 m s^{- 2}$ )
Hint
Compare the PE at the two heights.
Answer
$0.2 \times 10 \times (5 - 3.2) = 3.6$ J, mainly into heat (in the ball and floor) and sound.
Q5 · 1 mark · Very short answerHarder board level
What energy conversion takes place when the brakes of a moving bicycle are applied?
Hint
The brake blocks get warm.
Answer
Kinetic energy → heat energy (and a little sound).
Q6 · 1 mark · Assertion-reasonHarder board level
Assertion (A): In any energy conversion, the total amount of energy stays the same.
Reason (R): The energy converted into heat is destroyed.
(a) Both true and R explains A (b) Both true, R does not explain A (c) A true, R false (d) A false, R true
Hint
Is heat destroyed, or just spread out?
Answer
(c). The heat is not destroyed; it spreads into the surroundings.
Q7 · 3 marks · Short answerHOTS / competency
A hand-cranked torch is wound for 1 minute by a person supplying 3 W of mechanical power. Half of this becomes electrical energy, which runs an LED of 0.5 W. (a) Write the chain of conversions from the person's food to the light. (b) How long will the LED glow?
Hint
Energy in = power × time.
Answer
(a) Chemical (food) → kinetic (cranking) → electrical → light (+ heat). (b) Input $= 3 \times 60 = 180$ J; electrical $= 90$ J; time $= \frac{90}{0.5} = 180$ s (3 minutes).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Conversion in a microphone?Show answer
Sound → electrical.
2.Conversion in a burning candle?Show answer
Chemical → heat + light.
3.Conversion in an electric generator?Show answer
Mechanical → electrical.
4.Conversion in a solar cell?Show answer
Light → electrical.
5.A device takes 100 J and gives 60 J of useful energy. Wasted?Show answer
40 J.

Energy Conversions: Forms of Energy and Examples: frequently asked questions

What are the different forms of energy in the ICSE syllabus?

Mechanical (potential and kinetic), chemical, heat, light, sound, electrical and nuclear energy.

How do I find the energy conversion in a device?

Ask where the energy comes from (what runs down or is used up) and what useful form it becomes; then add any heat or sound wasted.

Is energy lost when it is converted?

No. Some becomes heat or sound that is not useful, but the total amount of energy stays the same.