AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Static charge: Two objects that carry the same type of charge repel.
Like charges repel: two negative objects push apart, and so do two positive ones.
- Point 6 of 9
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Like charges repel: two negative objects push apart, and so do two positive ones. In the standard demonstration a charged polythene rod is brought near an identical charged rod hanging from a thread, and the hanging rod swings away. The reason is that each rod sits in the electric field of the other, and a negative charge in the field of another negative charge is pushed outwards. Repulsion is the more useful test of the two, because attraction also happens between a charged object and an uncharged one, whereas only two like-charged objects repel. That is why the hair on a charged student's head stands up: every hair carries the same sign of charge, so the hairs repel and spread as far apart as they can.
What earns the marks
- Identifying the force as a force of repulsion.
- The reason that both objects carry the same type of charge.
- Repulsion, rather than attraction, being the reliable test for a charged object.
- Each hair carrying the same charge when explaining hair standing on end.
Common mistakes and how to put them right
Giving repulsion as the answer but then giving a reason about opposite charges.
Using attraction as proof that an object is charged, when an uncharged object is attracted too.
Saying the rods repel because they are both made of plastic.
Leaving the reason blank, when the reason mark depends on the first answer being right.
Exam tips
- In tick-box questions with a reason, the reason mark usually depends on the tick, so decide carefully first.
- State the sign of both charges in your reason, not simply that they are charged.
- Remember that repulsion is the only safe test for charge.
Try the lesson
The start of the Static charge: Two objects that carry the same type of charge repel. lesson, made from checked teaching notes for this specification point.
Have a go first
A student rubs two identical polythene rods with a woollen cloth. Both rods become negatively charged. When the rods are brought close together, what happens?
Listen
Like charges repel: two negative objects push apart, and so do two positive ones. In the standard demonstration a charged polythene rod is brought near an identical charged rod hanging from a thread, and the hanging rod swings away. The reason is that each rod sits in the electric field of the other, and a negative charge in the field of another negative charge is pushed outwards. Repulsion is the more useful test of the two, because attraction also happens between a charged object and an uncharged one, whereas only two like-charged objects repel. That is why the hair on a charged student's head stands up: every hair carries the same sign of charge, so the hairs repel and spread as far apart as they can. A strong answer earns marks for these points. identifying the force as a force of repulsion. the reason that both objects carry the same type of charge. repulsion, rather than attraction, being the reliable test for a charged object. each hair carrying the same charge when explaining hair standing on end. Exam tip: In tick-box questions with a reason, the reason mark usually depends on the tick, so decide carefully first.
Key words
Say what each word means before you turn the card.
like charges repel
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test for charge
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hanging rod demonstration
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See every definition
- like charges repel
- Two objects that carry the same type of charge push apart, because each sits in the electric field of the other and is pushed outwards.
- test for charge
- Repulsion is the more useful test, because attraction also happens between a charged object and an uncharged one, whereas only two like-charged objects repel.
- hanging rod demonstration
- A charged polythene rod is brought near an identical charged rod hanging from a thread, and the hanging rod swings away.
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