AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Energy stores and systems: work done when a current flows
When charge flows through a component, work is done.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
When charge flows through a component, work is done. Energy is transferred from the chemical store of a battery by the electrical working pathway to other stores, such as the thermal store of a resistor. The work done (energy transferred) can be calculated using E = Q × V, where Q is charge flow and V is potential difference. For example, a 12 V supply moving 10 C of charge transfers 12 × 10 = 120 J of energy. It is vital to distinguish between energy transfer pathways: electrical work transfers energy to the resistor's thermal store, while heating transfers energy from the hot resistor to the thermal store of the surroundings.
What earns the marks
- State that work is done when charge flows through a circuit component.
- Calculate work done using the equation E = Q × V, identifying energy, charge flow and potential difference.
- Use the correct units: potential difference in volts (V), charge in coulombs (C) and work done in joules (J).
- Distinguish between pathways: electrical work transfers energy to a component's thermal store, whereas heating transfers energy to the surroundings.
- Recognise that the work done by the current equals the energy transferred from the power supply.
Common mistakes and how to put them right
Conflating electrical work and heating.
Put it right: Electrical work is the pathway to the resistor, heating is the pathway from the resistor to the surroundings.
Using time instead of charge in the E = Q × V equation.
Put it right: Ensure charge flow in coulombs is used.
Assuming all the energy transferred by electrical work is useful.
Put it right: In a resistor, the energy increases the thermal store, which may be dissipated as wasted energy.
Exam tips
- Clearly state the energy stores and the pathways separately, e.g., 'electrical work transfers energy to the thermal store'.
- Write the equation E = Q × V, substitute values with units, then calculate and give the unit in joules.
Try the lesson
The start of the Energy stores and systems: work done when a current flows lesson, made from checked teaching notes for this specification point.
Have a go first
A current of 3.0 A flows through a motor for 20 s. The potential difference across the motor is 12 V. What is the work done by the current?
Listen
When charge flows through a component, work is done. Energy is transferred from the chemical store of a battery by the electrical working pathway to other stores, such as the thermal store of a resistor. The work done (energy transferred) can be calculated using E = Q × V, where Q is charge flow and V is potential difference. For example, a 12 V supply moving 10 C of charge transfers 12 × 10 = 120 J of energy. It is vital to distinguish between energy transfer pathways: electrical work transfers energy to the resistor's thermal store, while heating transfers energy from the hot resistor to the thermal store of the surroundings. A strong answer earns marks for these points. State that work is done when charge flows through a circuit component. Calculate work done using the equation E = Q × V, identifying energy, charge flow and potential difference. Use the correct units: potential difference in volts (V), charge in coulombs (C) and work done in joules (J). Distinguish between pathways: electrical work transfers energy to a component's thermal store, whereas heating transfers energy to the surroundings. Exam tip: Clearly state the energy stores and the pathways separately, e.g., 'electrical work transfers energy to the thermal store'.
Key words
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Electrical energy transfer
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Charge and potential difference
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Energy pathways vs stores
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Energy conservation and dissipation
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See every definition
- Electrical energy transfer
- Work is done when charge flows through a circuit component, transferring energy from the power supply.
- Charge and potential difference
- Work done can be calculated using E = Q × V, where Q is charge flow and V is potential difference.
- Energy pathways vs stores
- Electrical work transfers energy to a component's thermal store, whereas heating transfers energy to the surroundings.
- Energy conservation and dissipation
- In a resistor, energy transferred by electrical work increases the thermal store, which may be dissipated as wasted energy.
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