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AQA GCSE Physics · Topic 4.2 Electricity
Static Electricity and Electric Fields
Physics only This whole page is for separate (triple) Physics.
Combined Science students don't need it.
In this lesson you'll learn to: explain how rubbing two insulators together makes them charged by
moving electrons, describe how a spark forms when the potential difference is big enough, draw the
electric field around a charged sphere, and explain how the force on a charge changes with distance.
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Prefer to watch? Scroll to the bottom for the video on this topic
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A video walkthrough is coming soon — it will appear at the bottom of this page
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Start here — have a play
Don't read anything yet. On tab 1, rub the balloon on the jumper and watch which way the electrons go, then switch on the Van de Graaff generator. On tab 2, build up charge until a spark jumps, then try again with the object earthed. On tab 3, drop a charge close to the sphere, then far away, and compare.
Example
What happens
Only electrons move. The positive charges (protons) are stuck in the nuclei. An object that gains electrons becomes negative; an object that loses electrons becomes positive.
Example
Two areas with different charge have a potential difference between them. When the p.d. is big enough, electrons jump across the air gap: that sudden flow of charge is the spark.
Charged sphere
Click anywhere in the field to drop in a small positive charge
Field lines point the way a positive charge would move: away from a positive sphere, towards a negative one. Where the lines are closer together the field is stronger: a bigger force, so (F = m a) a bigger acceleration.
Not to scale: real objects hold billions of extra electrons.
▲ Only the electrons ever move. The positive charges stay where they are.
Seen the electrons jump? Now explain it in words.
Static questions want a chain of steps in the right order: friction → electrons move → charged → p.d. → spark. The notes below give you each chain.
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Revision notes
4.2.5.1 Static charge
When two insulating materials are rubbed together, friction does work on the electrons and electrons move from one object to the other.
−
Gains electrons
More electrons than protons, so it becomes negatively charged. (The balloon.)
+
Loses electrons
Fewer electrons than protons, so it becomes positively charged. (The jumper.)
⭐ Only electrons move
Never write that "positive charges move" or "protons move". The protons are fixed in the nuclei; an object becomes positive by losing electrons.
- Like charges repel; unlike charges attract. These forces act without the objects touching.
- A Van de Graaff generator uses a rubber belt and a plastic roller. Electrons are carried away from the dome to earth, so the dome is left positively charged.
Sparks
As charge builds up on an object, the potential difference between the object and earth increases. If the p.d. is big enough, electrons jump through the air to the earthed conductor. That sudden flow of charge is a spark.
| Example | Charged object | Earthed object |
|---|---|---|
| Shock from a tap | a person who has walked on a nylon carpet | the metal tap |
| Fuel spark | a car (or a fuel hose) | the petrol nozzle and pump |
At a petrol station a spark could ignite the petrol vapour. Earthing gives the charge a path to flow away, so it never builds up and no spark forms.
4.2.5.2 Electric fields
⭐ Definition
An electric field is a region where a charged object experiences a force.
- The field is strongest close to the sphere, where the lines are closest together.
- A second charged object in the field feels a force. The closer it is, the bigger the force.
- Using F = m a: a bigger force gives a bigger acceleration (the mass stays the same).
- A spark happens when the field is strong enough to make the air conduct.
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How to write it in the exam
The chain for "how does it become charged?"
The two objects are rubbed together, so friction moves
electrons from one to the other. The object that gains electrons becomes
negative; the object that loses electrons becomes positive.
what happenswhat movesthe result
Exam-style question · charging · 3 marks
A girl pulls a wool jumper off over her head. Her hair gains electrons and stands on end. Explain why.
- Friction moves electrons from the jumper onto her hair (1)
- so every hair is negatively charged (1)
- like charges repel, so the hairs push away from each other (1)
Where marks go missing: "positive charges move". Only electrons move.
Exam-style question · sparks · 3 marks
A child slides down a plastic slide and gets a shock when touching the metal frame. Explain why.
- Friction moves electrons, so charge builds up on the child (1)
- so there is a large potential difference between the child and the earthed frame (1)
- electrons jump between them: a spark / shock (1)
Exam-style question · fields · 3 marks
A small positive charge is released near a negatively charged sphere. Describe and explain how its acceleration changes as it moves.
- It is attracted towards the sphere (unlike charges) (1)
- As it gets closer the field lines are closer together, so the field is stronger and the force is bigger (1)
- From F = m a, a bigger force gives a bigger acceleration (1)
📘 Now do it in your workbook
Explain how objects become charged and how sparks form, work through the balloon and petrol station questions, then draw the field around charged spheres.
AQA GCSE Physics Workbook · ELECTRICITY · pages 16, 17 & 18The full workbook covers the whole of Topic 4.2 Electricity, with exam-style questions and worked answers.
✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this spec point.
Don't forget to hit “Mark complete” at the bottom of the lesson.
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Prefer to watch? Here's the whole thing
Video walkthrough — coming soon
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it.
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it. The video is on its way.
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Video coming soon
The walkthrough for this lesson is being filmed and will appear right here. Until then, the animation and the notes above cover every mark.
Now put it into practice
Pages 16, 17 and 18 of the workbook have the charging and spark chains, the balloon and petrol station questions and the field diagrams, with full answers at the back.
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