Electric fields — AQA GCSE Physics
Test yourself on Electric fields with AQA GCSE practice questions.
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Electric fields explained
Bring two charged objects closer and the force between them grows, because the second object moves into a region where the first object's field is stronger.
Read the full explanation
The increase is steep rather than steady, since halving the separation does far more than double the force, which is why a charged rod feels like nothing at arm's length but snatches at a scrap of paper a centimetre away. The same rule governs sparking: as an earthed conductor is moved towards a charged dome, the field in the gap grows stronger until the air breaks down. Notice that the two objects always feel forces of the same size however different they are, so the small object does not feel a bigger force just because it is the one that moves.
Your focus
- Explain why a spark jumps only once an earthed conductor has been brought close to a charged dome, referring to the potential difference across the gap and the breakdown of the air.
- Explain the rise in force as the separation falls, using the strength of the field in which the second object sits.
- Explain why both objects feel forces of equal size even when only one of them moves.
Electric fields exam tips
Marking Points
- one mark for the force increasing as the separation decreases
- one mark for explaining this as the second object moving into a stronger region of the field
- one mark for the two objects always experiencing forces equal in size and opposite in direction
- one mark for linking the stronger field at small separation to the air breaking down and a spark forming
Examiner Tips
- 💡Write 'increases' and give the field reason, because a bare 'gets bigger' may not earn the explanation mark.
- 💡Remember the forces on the two objects stay equal in size even when only one of them moves.
- 💡Link a spark question back to the field in the gap rather than to the distance alone.
Common Mistakes
- describing the increase as directly proportional to the decrease in distance
- saying the lighter object feels the larger force because it accelerates more
- claiming the force only appears once the objects touch
- confusing the strengthening field with an increase in the charge on the objects