IGCSE Physics revision · Electricity & magnetism
Static electricity
One idea decides every mark on this topic: only electrons move. Every explanation of charging — rods, cloths, balloons, fuel trucks — is a sentence about electrons being transferred, never about positive charge moving.
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What the syllabus demands
- —Describe charging by friction as the transfer of electrons
- —State that like charges repel and unlike charges attract
- —Describe simple experiments to show attraction and repulsion
- —Distinguish conductors from insulators
- —Sketch the electric field patterns around a point charge and between parallel plates (Extended)
Definitions that earn marks
Clear definitions to practise — check your course mark scheme
- Charging by friction
- The transfer of electrons from one material to another by rubbing: the material gaining electrons becomes negative, the one losing electrons becomes positive.
- Electric field
- A region in which an electric charge experiences a force. Field lines point in the direction of the force on a positive charge.
- Conductor
- A material that allows charge (electrons) to flow through it easily.
- Insulator
- A material through which charge cannot flow — which is why it can hold static charge.
Where the marks die
Common mistakes to check
- 01
Saying positive charge moves. Protons are locked in the nucleus. A material becomes positive by losing electrons — never by gaining protons. This single sentence is the most repeated mark on the topic.
- 02
Forgetting that a charged object can attract an uncharged one — by inducing charge separation in it. Attraction alone does not prove the second object is charged.
- 03
Explaining static hazards without the spark: charge builds up, the potential difference grows, and eventually a spark can ignite fuel vapour. The prevention: an earthing wire lets the charge flow safely away.
- 04
Drawing field lines with no arrows, or pointing towards a positive charge. Field lines point away from positive and towards negative.
One worked example, done properly
Question
A polythene rod is rubbed with a cloth and becomes negatively charged. Explain what has happened, and state the charge on the cloth.
Method
- 1.Rubbing transfers electrons from the cloth to the rod.
- 2.The rod gains electrons, becoming negatively charged.
- 3.The cloth loses the same number of electrons.
The cloth becomes equally positively charged — charge is conserved.