Static Electricity [H]

This lesson covers static electricity — the build-up and discharge of electric charge on insulating materials. This topic is part of the AQA GCSE Physics specification (4.2.5) and is Higher Tier only content, indicated by [H]. You must understand how static charge is produced, how electric fields work, and the dangers and uses of static electricity.

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What Is Static Electricity?

Static electricity is the build-up of electric charge on the surface of an object, typically an insulator. Unlike current electricity (where charge flows continuously through a conductor), static charge stays in one place — it is "static" (stationary).

Static charge is produced by the transfer of electrons between objects when they are rubbed together (friction).

Key Principles

• All matter contains positive charges (protons in the nucleus) and negative charges (electrons orbiting the nucleus).
• In a neutral object, the number of protons equals the number of electrons — the charges balance.
• When two insulating materials are rubbed together, electrons are transferred from one surface to the other.
• The material that loses electrons becomes positively charged.
• The material that gains electrons becomes negatively charged.

Important: It is always electrons that move, never protons. Protons are fixed in the nucleus and cannot be transferred by rubbing.

Object	Electrons	Charge
Material that loses electrons	Fewer electrons than protons	Positive
Material that gains electrons	More electrons than protons	Negative

Exam Tip: When explaining how an object becomes charged, always state that "electrons are transferred" (not "charge is transferred" or "protons are transferred"). The AQA mark scheme specifically requires you to mention electrons. Also, state which way the electrons move and which object becomes positive/negative.

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Examples of Static Electricity

Rubbing a Polythene Rod with a Cloth

1. When a polythene rod is rubbed with a cloth, electrons are transferred from the cloth to the polythene rod.
2. The polythene rod gains electrons and becomes negatively charged.
3. The cloth loses electrons and becomes positively charged.

Rubbing an Acetate Rod with a Cloth

1. When an acetate rod is rubbed with a cloth, electrons are transferred from the acetate rod to the cloth.
2. The acetate rod loses electrons and becomes positively charged.
3. The cloth gains electrons and becomes negatively charged.

Everyday Examples

Phenomenon	Explanation
Hair standing on end when combed	Electrons transfer between the comb and hair; same-charged hairs repel each other
Clothing clings after tumble-drying	Friction between fabrics transfers electrons; oppositely charged items attract
Electric shock from car door	Friction between clothing and car seat builds up charge; discharge occurs when you touch the metal door
Lightning	Charge separation in clouds due to friction between ice particles; massive discharge between cloud and ground
Balloon sticking to a wall	Rubbing the balloon on clothing gives it a charge; it induces an opposite charge on the wall surface and is attracted

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Forces Between Charged Objects

Charged objects exert non-contact forces on each other:

• Like charges repel — two positive charges or two negative charges push each other away.
• Unlike charges attract — a positive charge and a negative charge pull each other together.

Interaction	Result
Positive + Positive	Repel
Negative + Negative	Repel
Positive + Negative	Attract
Charged + Neutral	Attract (due to induction)

Attraction of a Charged Object to a Neutral Object

A charged object can attract a neutral object. This happens because of electrostatic induction:

1. The charged object causes the charges in the neutral object to redistribute.
2. The opposite charges in the neutral object are drawn closer to the charged object.
3. The same-type charges in the neutral object are pushed further away.
4. Because the opposite charges are now closer, the attractive force is stronger than the repulsive force, resulting in a net attraction.

Exam Tip: "Like charges repel, unlike charges attract" is a fundamental rule. A common exam mistake is to say that a charged object repels a neutral object — it does not. A charged object always ATTRACTS a neutral object (by induction).

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Electric Fields [H]

An electric field is the region around a charged object where another charged object would experience a force. Electric fields are a non-contact force field.

Properties of Electric Fields

• The electric field gets stronger as you get closer to the charged object.
• Electric field lines show the direction a positive test charge would move if placed in the field.
• Field lines point away from positive charges and toward negative charges.
• The closer together the field lines, the stronger the field.
• Electric field lines never cross each other.

Electric Field Patterns

Single positive charge: Field lines radiate outward in all directions (like the spokes of a wheel).

Single negative charge: Field lines point inward from all directions toward the charge.

Two parallel plates (uniform field): Between two oppositely charged parallel plates, the field lines are parallel, equally spaced and perpendicular to the plates. This creates a uniform electric field (same strength everywhere between the plates).

graph LR
    subgraph Uniform Field Between Parallel Plates
    A["+ Plate"] --> B["Field lines pointing from + to -"]
    B --> C["- Plate"]
    end

Exam Tip: When drawing electric field lines, always include arrowheads showing the direction (from positive to negative). The lines must start and end on the surfaces of the charged objects (or extend to infinity for isolated charges). Do not draw field lines crossing each other.

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Electrostatic Discharge

When a charged object comes close to (or touches) a conductor connected to earth, the charge can discharge — the electrons flow rapidly from the charged object to earth (or from earth to the object), neutralising the charge.

This discharge can cause:

• A spark (visible flash of light)
• A shock (if a person is involved)
• An explosion (if flammable gases or vapours are present)
• Damage to electronic components (sensitive microchips can be destroyed by static discharge)

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Dangers of Static Electricity