A student sets up a circuit containing a battery, a motor, and a lamp connected in series. The motor is used to lift a small weight. Explain how energy is transferred from the battery to the surroundings in this circuit, including the role of potential difference.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The battery has a potential difference of 6 V. The potential difference across the motor is 4 V and the potential difference across the lamp is 2 V.
Model answer (4 marks)
The battery supplies a potential difference of 6 V, meaning each coulomb of charge gains 6 J of energy.
1. The 6 V is divided between the motor (4 V) and the lamp (2 V) because they are in series.
2. The 4 V across the motor converts the electrical energy into kinetic energy of the motor’s shaft, which lifts the weight.
3. The 2 V across the lamp is used to heat the filament and produce light.
4. Thus the chemical energy stored in the battery becomes electrical energy, then is split into mechanical work (lifting) and thermal/light energy, all driven by the potential differences.
1. The 6 V is divided between the motor (4 V) and the lamp (2 V) because they are in series.
2. The 4 V across the motor converts the electrical energy into kinetic energy of the motor’s shaft, which lifts the weight.
3. The 2 V across the lamp is used to heat the filament and produce light.
4. Thus the chemical energy stored in the battery becomes electrical energy, then is split into mechanical work (lifting) and thermal/light energy, all driven by the potential differences.
Examiner tips
- Show the voltage division 4 V+2 V=6 V; link each p.d. to the energy form produced.
- Use the phrase ‘chemical energy → electrical energy → mechanical/thermal energy’ to match the scheme.
- Mention the battery’s role as the source of potential difference.
- Keep the answer concise – 4 short points for 4 marks.
Common mistakes
- Confusing voltage with current; forgetting that the sum of p.d.s equals the battery’s p.d.
- Not specifying which energy form is produced by each component.
- Using vague terms like ‘energy’ without indicating the type (mechanical, thermal, light).
Mark scheme (4 marks)
- The potential difference (voltage) is a measure of the energy transferred per unit charge / work done per unit charge between two points in the circuit.
- The sum of the potential differences across the motor and the lamp equals the potential difference of the battery / the p.d.s across the components share the total p.d. of the supply (4 V + 2 V = 6 V).
- Chemical energy in the battery is transferred to electrical energy, which is then transferred to kinetic / mechanical energy by the motor (to lift the weight).
- The lamp transfers electrical energy to thermal energy (and light energy) / current does work against the resistance of the lamp, producing heat and light.
Key terms in this question
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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