4.2.5

Electrical energy and electrical power

Cambridge IGCSE Physics (0625)  · Unit 4: Electricity and magnetism  · 8 flashcards

Electrical energy and electrical power is topic 4.2.5 in the Cambridge IGCSE Physics (0625) syllabus , positioned in Unit 4 — Electricity and magnetism , alongside Simple phenomena of magnetism, Electric charge and Electric current.  In one line: The kilowatt-hour (kWh) is a unit of energy.

It measures the amount of electrical energy used by a 1 kilowatt (kW) device operating for 1 hour.

1 kWh is equivalent to 3,600,000 Joules (J). It relates power (kW) and time (h) to energy consumed.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).

The deck below contains 8 flashcards — 1 definition — covering the precise wording mark schemes reward.  Use the definition card to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

The kilowatt-hour (kWh). Explain what it measures and what units it relates to

The kilowatt-hour (kWh) is a unit of energy.

It measures the amount of electrical energy used by a 1 kilowatt (kW) device operating for 1 hour.

1 kWh is equivalent to 3,600,000 Joules (J). It relates power (kW) and time (h) to energy consumed.

What the Cambridge 0625 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Understand Understand that electric circuits transfer energy from a source of electrical energy, such as an electrical cell or mains supply, to the circuit components and then into the surroundings
  2. Recall Recall and use the equation for electrical power
  3. Recall Recall and use the equation for electrical energy
  4. Define Define the kilowatt-hour (kWh) and calculate the cost of using electrical appliances where the energy unit is the kWh
Key Concept Flip

A torch uses a battery to light a bulb. Explain how energy is transferred in this circuit, starting from the battery.

Answer Flip

1. The battery stores chemical energy.
2. This chemical energy is converted into electrical energy in the circuit.
3. The electrical energy is transferred to the bulb.
4. At the bulb, electrical energy is converted into light energy and thermal energy (heat), which are released into the surroundings.

Key Concept Flip

State two energy transfers that occur when an electric heater is switched on.

Answer Flip

1. Electrical energy to thermal energy (heating the element).
2. Thermal energy to the surroundings (through convection and radiation).

Key Concept Flip

A lamp is connected to a 12V power supply. If the current flowing through the lamp is 0.5A, calculate the power consumed by the lamp.

Answer Flip

Power (P) = Voltage (V) x Current (I)
P = 12V x 0.5A
P = 6W

Therefore, the power consumed by the lamp is 6 Watts. This means the lamp is converting 6 Joules of electrical energy into light and heat energy every second.

Key Concept Flip

State the equation that relates electrical power, voltage, and current. Briefly explain what each term represents.

Answer Flip

Power (P) = Voltage (V) x Current (I)

P (Power): The rate at which electrical energy is converted into other forms of energy (

Example: heat, light). Measured in Watts (W).<br>V (Voltage): The electrical potential difference across a component. It is the energy required to move a unit charge through the component. Measured in Volts (V).<br>I (Current): The rate of flow of electrical charge through a component. Measured in Amperes (A).
Key Concept Flip

A 6V torch bulb has a current of 0.5A flowing through it. Calculate the electrical energy transferred in 2 minutes.

Answer Flip

Electrical energy = Voltage x Current x Time
E = V x I x t
E = 6V x 0.5A x (2 x 60)s
E = 360 J

Explanation: The formula E=VIT is used to calculate electrical energy transformed, and the time is converted into seconds before using it in the equation.

Key Concept Flip

A heater transfers 7200J of electrical energy when connected to a 240V mains supply for 1 minute. What current flows through the heater?

Answer Flip

Electrical energy = Voltage x Current x Time
E = V x I x t
7200J = 240V x I x 60s
I = 7200J / (240V x 60s)
I = 0.5A

Explanation: First rearrange the energy equation to solve for current (I=E/VT).

Key Concept Flip

An electric heater is rated at 2.0 kW. It is used for 3 hours per day for 30 days. Calculate the total cost of using the heater if electricity costs $0.20 per kilowatt-hour (kWh).

Answer Flip

1. Calculate total energy consumption:
Energy (kWh) = Power (kW) × Time (hours)
Energy = 2.0 kW × 3 hours/day × 30 days = 180 kWh

2. Calculate total cost:
Cost = Energy (kWh) × Cost per kWh
Cost = 180 kWh × $0.20/kWh = $36.00

Answer: The total cost of using the heater is $36.00

Definition Flip

Define the kilowatt-hour (kWh). Explain what it measures and what units it relates to.

Answer Flip

The kilowatt-hour (kWh) is a unit of energy.

It measures the amount of electrical energy used by a 1 kilowatt (kW) device operating for 1 hour.

1 kWh is equivalent to 3,600,000 Joules (J). It relates power (kW) and time (h) to energy consumed.

Review the material

Read revision notes with definitions, equations, and exam tips.

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Test yourself

Practice with MCQ questions to check your understanding.

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4.2.4 Resistance 4.3.1 Circuit diagrams and circuit components

Key Questions: Electrical energy and electrical power

Define the kilowatt-hour (kWh). Explain what it measures and what units it relates to.

The kilowatt-hour (kWh) is a unit of energy.

It measures the amount of electrical energy used by a 1 kilowatt (kW) device operating for 1 hour.

1 kWh is equivalent to 3,600,000 Joules (J). It relates power (kW) and time (h) to energy consumed.

More topics in Unit 4 — Electricity and magnetism

Electrical energy and electrical power sits alongside these Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

4.1 Simple phenomena of magnetism

22 flashcards
4.2.1 Electric charge

20 flashcards
4.2.2 Electric current

12 flashcards
4.2.3 Electromotive force and potential difference

14 flashcards
4.2.4 Resistance

10 flashcards
4.3.1 Circuit diagrams and circuit components

4 flashcards
4.3.2 Series and parallel circuits

24 flashcards
4.3.3 Action and use of circuit components

6 flashcards
4.4 Electrical safety

10 flashcards
4.5.1 Electromagnetic induction

10 flashcards
4.5.2 The a.c. generator

4 flashcards
4.5.3 Magnetic effect of a current

10 flashcards
4.5.4 Force on a current-carrying conductor

6 flashcards
4.5.5 The d.c. motor

4 flashcards
4.5.6 The transformer

16 flashcards

Key terms covered in this Electrical energy and electrical power deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

The kilowatt-hour (kWh). Explain what it measures and what units it relates to

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How to study this Electrical energy and electrical power deck

Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.