Electricity and magnetism · GCSE Physics
Static electricity
Teacher-written GCSE Physics revision on static charge: friction, electron transfer, electrostatic forces, electric fields, uses such as photocopiers, and dangers near fuels.
Like charges repel; unlike attract. Friction moves electrons — the insulator keeps them. Sparks mean a big enough potential difference has built up.
The important bits
What you need to know
- 1
Static electricity is a build-up of electric charge on an insulator when electrons are transferred by friction. The material that gains electrons becomes negatively charged; the one that loses them becomes positively charged.
- 2
Only electrons move in GCSE models — protons stay in nuclei. Charge is measured in coulombs (C). Like charges repel; unlike charges attract.
- 3
An object can be charged by friction (rubbing), induction (bringing a charged rod near a conductor, then earthing), or contact. Insulators hold charge; conductors allow charge to move through them.
- 4
A gold-leaf electroscope detects charge: like charge on the cap and leaf repels, so the leaf rises. A spark is a rapid discharge when potential difference is large enough to ionise air.
- 5
An electric field surrounds charged objects. Field lines go from positive to negative. A charged object in a field experiences a force without contact — non-contact electrostatic force.
- 6
Uses: photocopiers and laser printers (charge patterns on drum attract toner); spray painting (charged paint droplets spread evenly); electrostatic precipitators remove dust from factory smoke.
- 7
Dangers: sparks near flammable vapours or powders (petrol stations, flour mills) can ignite explosions. Earthing (bonding) and antistatic materials discharge charge safely. Fuel hoses are earthed.
- 8
Static is not the same as current in a circuit: no continuous flow until discharge. Lightning is a large-scale discharge. Humidity reduces static because water on surfaces allows charge to leak away.
Quotations worth analysing
Short evidence. Real method.
“When two insulating materials are rubbed together, electrons are transferred from one to the other.”
Name which material gained or lost electrons if the question gives the series (e.g. polythene rod with wool). Do not say “protons move”.
“Like charges repel; unlike charges attract.”
Apply to electroscope, hair standing on end, or paper attracted to a charged comb — always pair the sign of charge with the force direction.
“Earthing provides a path for charge to flow to the ground safely.”
Use in petrol station and hospital operating theatre contexts. Bonding connects conductors so no dangerous p.d. builds between them.
Go deeper
Friction and the electron story
Rub a polythene rod with a cloth: electrons leave the cloth and sit on the rod — rod negative, cloth left positive. Rub an acetate rod: electrons leave the rod — rod positive. The triboelectric series tells you direction if you learn a pair. Charge stays on an insulator because electrons cannot move freely through the material. Bring the rod near small pieces of paper: polarisation induces opposite charge on the near side of the paper, attraction follows. If the exam asks why dust sticks to a TV screen, same idea — induced charge on an insulator surface. Always electrons transferred; positive charge means fewer electrons, not moving protons.
Go deeper
Induction and earthing in one diagram
Bring a negative rod near a metal sphere on an insulator. Electrons in the sphere are repelled to the far side — near side looks positive by induction. Touch the far side with a finger (earth): electrons leave to ground. Remove finger, then remove rod: sphere is left positive. Induction lets you charge without contact. Earthing is the safety version: connect the conductor to ground so charge cannot accumulate to spark level. Petrol tankers drag chains or use earthing cables before loading so static from flow does not ignite vapour. Flour mills use earthing, humidity control, and no sparking switches — airborne powder plus spark equals explosion risk.
Go deeper
Uses versus hazards — write both sides
Photocopiers charge a drum selectively; toner sticks to charged areas and is fused to paper — static as tool. Spray painting charges paint and object oppositely for even coat and less waste. Precipitators charge smoke particles, which collect on plates — cleaner air. Hazards: any high p.d. across an insulator in oxygen-rich or vapour-rich air can spark. Lightning is static at scale: cloud separation of charge, discharge to ground. Evaluation answers name the application or the hazard, the physics (charge build-up, discharge), and the engineering fix (earth, resistor, antistatic flooring). Do not confuse static build-up with mains electricity — different chapter, same word “electric”.
See the idea in action
A student rubs a polythene rod with a wool duster. Electrons transfer to the rod; the rod becomes negatively charged. When held near a neutral metal can on an insulator, electrons in the can are repelled to the far side — the near face is induced positive and the can is attracted. If the rod is then earthed while the charged rod is held nearby, charge on the can can be removed safely. At a petrol pump, earthing the nozzle and tanker prevents a spark that could ignite vapour.
Exam technique
Turn knowledge into marks
Every static answer: what moved (electrons), which sign resulted, like/unlike force or spark risk. For safety, say earthing or bonding and name the flammable context.
Common mistakes
Do not give these marks away
- 01
Saying protons move during rubbing, or that positive charge is added as a separate substance.
- 02
Confusing static charge on an insulator with current in a metal wire circuit.
- 03
Ignoring earthing in petrol or flour-mill questions — the mark is often the engineering fix.
Why must fuel tankers be earthed when unloading?
ATo increase the current in the engine
BTo stop static charge building up and sparking, which could ignite flammable vapour
CTo make the petrol flow faster by gravity
DBecause petrol is a metal conductor
Show the answer
To stop static charge building up and sparking, which could ignite flammable vapour. Flowing fuel can separate charge. Earthing gives electrons a safe path so potential difference cannot reach spark level.
Quick questions
If this is the bit you searched
What charge moves when materials are rubbed?
Electrons transfer from one material to the other. The one that gains electrons becomes negative; the one that loses them becomes positive.
What is an electroscope used for?
To detect charge. Like charge on the leaf and cap causes repulsion and the leaf rises.
How is static used in photocopiers?
A charged drum attracts toner in a pattern; heat fuses toner to paper. Charge controls where ink sticks.
Why is static dangerous in flour mills?
Fine flour dust in air is explosive if ignited. Static sparks from equipment can trigger ignition — earthing and humidity reduce the risk.