Static Electricity

This lesson covers static electricity — the build-up and transfer of electric charge on insulating materials — as required by AQA GCSE Combined Science Trilogy (8464, section 6.2.1). While static electricity does not flow like current electricity, it is an important topic that connects to the fundamental concepts of charge.

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What Is Static Electricity?

Static electricity is the build-up of electric charge on the surface of an object. Unlike current electricity (where charge flows continuously through a conductor), static charge stays stationary on the surface of an insulator — it does not flow away because insulators do not allow charge to move freely.

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How Does Static Charge Build Up?

Static electricity is produced by friction — when two insulating materials are rubbed together. During rubbing:

1. Electrons are transferred from one material to the other.
2. The material that gains electrons becomes negatively charged.
3. The material that loses electrons becomes positively charged.

Important: It is only electrons that move. Protons are fixed in the nucleus of atoms and cannot be transferred by rubbing.

Example: Rubbing a Polythene Rod with a Cloth

Object	What happens	Charge
Polythene rod	Gains electrons from the cloth	Becomes negatively charged
Cloth	Loses electrons to the rod	Becomes positively charged

Example: Rubbing an Acetate Rod with a Cloth

Object	What happens	Charge
Acetate rod	Loses electrons to the cloth	Becomes positively charged
Cloth	Gains electrons from the rod	Becomes negatively charged

Exam Tip (AQA 8464): The total charge is conserved — the positive charge gained by one object is exactly equal to the negative charge gained by the other. No charge is created or destroyed; it is simply transferred.

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Attraction and Repulsion

Interaction	Result
Two positive charges	Repel
Two negative charges	Repel
A positive and a negative charge	Attract

The key rule:

Like charges repel; unlike (opposite) charges attract.

A charged object can also attract a neutral (uncharged) object. This happens because the charged object induces (rearranges) the charges on the surface of the neutral object, pulling opposite charges closer.

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Why Insulators Hold Static Charge

• In an insulator, electrons are tightly bound to atoms and cannot move freely.
• When charge is deposited on an insulator's surface, it stays there — it cannot flow away.
• In a conductor, free electrons can move easily, so any charge placed on the surface quickly flows away to earth (if the conductor is earthed).

This is why you can build up static charge by rubbing a plastic ruler (insulator) but not a metal rod (conductor — unless it is held by an insulating handle).

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Electric Fields

A charged object creates an electric field around it. Any other charged object placed in this field will experience a force.

• The field is strongest close to the charged object.
• The field gets weaker with increasing distance.
• Field lines point away from positive charges and toward negative charges.

For AQA Combined Science, you do not need to draw detailed field diagrams, but you must understand that:

• Charged objects exert non-contact forces on each other through electric fields.
• The force can be attractive (opposite charges) or repulsive (like charges).

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Dangers of Static Electricity

Lightning

1. Ice crystals in clouds rub together, causing a build-up of charge.
2. The bottom of the cloud becomes negatively charged.
3. This induces a positive charge on the ground below.
4. When the voltage becomes large enough, the air is ionised and a huge spark (lightning) jumps between the cloud and the ground.

Sparks from Fuelling

• When fuel flows through a pipe, friction between the fuel and the pipe can cause a build-up of static charge.
• A spark could ignite the fuel vapour, causing a fire or explosion.
• Prevention: The fuelling equipment is earthed using a conductive strap, so charge flows safely to the ground instead of building up.

Electric Shock from Everyday Objects

• Walking across a synthetic carpet can cause electrons to transfer to your body.
• When you touch a metal object (like a door handle), the charge discharges rapidly as a small spark — you feel a mild shock.

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Uses of Static Electricity

Electrostatic Precipitator (Removing Smoke Particles)

1. Smoke particles pass through a chimney containing charged metal plates or wires.
2. The smoke particles pick up a negative charge.
3. The negatively charged particles are attracted to positively charged collecting plates.
4. The particles stick to the plates and are periodically knocked off and collected.

Electrostatic Spray Painting

1. The paint is given a charge as it leaves the spray gun.
2. The object to be painted is given the opposite charge (or is earthed).
3. The charged paint droplets are attracted to the object, giving an even coat.
4. Less paint is wasted because the droplets are attracted to the object rather than flying past it.

Photocopier / Laser Printer

• Uses charged surfaces to attract toner (ink powder) to specific areas of a drum, which is then transferred to paper.

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Worked Examples

Worked Example 1

A polythene rod is rubbed with a cloth. The rod gains a charge of −3 nC. What charge does the cloth gain?

Charge is conserved, so the cloth gains a charge of +3 nC.

Worked Example 2

Two charged balloons are brought close together. Both have a negative charge. What happens?

Like charges repel — the balloons move apart.

Worked Example 3

A charged plastic comb is brought near small pieces of paper. The paper is uncharged. What happens and why?

The charged comb attracts the paper. The charge on the comb induces (rearranges) the charges in the paper — the side nearest the comb has the opposite charge, so it is attracted.

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Common Mistakes

Mistake	Correction
Saying "protons are transferred"	Only electrons are transferred — protons are fixed in the nucleus
Saying a charged object "has extra charge" without specifying type	Always say whether it has gained electrons (negative) or lost electrons (positive)
Saying conductors cannot be charged	Conductors can be charged but the charge flows away unless they are insulated from earth
Confusing static charge with current	Static charge is stationary on an insulator's surface; current is a continuous flow of charge through a conductor

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Summary