Static Electricity

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CognitoStatic electricity and electric fields

Key facts & equations

Charging by friction

When two insulators are rubbed together, electrons are transferred from one to the other.
Object that gains electrons: becomes negatively charged.
Object that loses electrons: becomes positively charged.
Like charges repel. Unlike charges attract.
Charge is measured in coulombs (C). Q = It.
Insulators hold charge on their surface; conductors allow charge to spread or flow away.

Electric fields

Any charged object creates an electric field around it.
The field shows the direction a positive test charge would move.
Field lines: radially outward from positive charge, inward to negative charge.
Between parallel plates: uniform field (parallel lines, equal spacing).
Stronger field = closer field lines. Field direction = direction of force on positive charge.

Hazards of static electricity

Sparks: if charge builds up, it can discharge suddenly → spark → fire/explosion risk.
Aircraft refuelling: metal bonding wire connects aircraft to ground to prevent sparks.
Grain/flour silos: fine particles can become charged → spark → explosion.
Petrol tankers: earthing the tanker prevents charge buildup when pouring fuel.
Medical: defibrillators use electric shock; static can damage electronic components.

Uses of static electricity

Inkjet printers: charged ink droplets deflected by electric field → precise positioning.
Photocopiers/laser printers: photoconductor drum charged, image-exposed areas lose charge, toner sticks to charged areas.
Electrostatic precipitator: charged plates attract charged soot/dust particles → cleaner air from chimneys.
Spray painting: charged paint droplets attracted to earthed car body → even coating, reduced waste.

Exam questions — 5 questions · 11 marks · AQA 8463 style

1 markCharging by frictionAQA 8463 style

When a plastic rod is rubbed with a cloth, the rod becomes negatively charged. What has happened?

A Protons have moved from the cloth to the rod

B Electrons have moved from the cloth to the rod

C Neutrons have moved between the rod and cloth

D The rod has created new negative charges by friction

3 marksElectrostatic precipitatorAQA 8463 style

Explain how an electrostatic precipitator removes soot particles from chimney gases. (3 marks)

Hint: Stage 1: particles are charged by the wire. Stage 2: charged particles attracted to plates. Stage 3: particles collected on plates and removed.

+30 XP

1 markUse of staticAQA 8463 style

Why are car bodies earthed during spray painting?

A To prevent the paint from becoming too thick

B So that the charged paint droplets are attracted to the car body — giving an even coat with less waste

C To prevent the car body from becoming magnetised during painting

D To ensure the paint dries faster

3 marksRefuelling hazardAQA 8463 style

Explain why aircraft are earthed with a metal bonding wire before refuelling, and what would happen without it. (3 marks)