Static Electricity

This lesson covers static electricity — as required by the Edexcel GCSE Physics specification (1PH0). You need to understand how objects become charged, the forces between charged objects, and the applications and dangers 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. Unlike current electricity (where charge flows continuously through a circuit), static charge stays in one place — it is stationary (hence "static").

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How Do Objects Become Charged?

Objects become charged by friction — when two different insulating materials are rubbed together.

The Process

1. When two insulating materials are rubbed together, electrons are transferred from one material to the other.
2. The material that gains electrons becomes negatively charged (it has more electrons than protons).
3. The material that loses electrons becomes positively charged (it has more protons than electrons).

Key Points

• Only electrons are transferred — protons are fixed in the nucleus of atoms and cannot move between materials.
• The total amount of charge is conserved — no charge is created or destroyed, it is simply transferred from one object to another.
• Only insulating materials can hold static charge on their surface. Conductors allow charge to flow away to earth.

What Happens	Resulting Charge
Object gains electrons	Negative charge
Object loses electrons	Positive charge

Common Examples

Materials Rubbed Together	Electron Transfer	Results
Polythene rod rubbed with cloth	Electrons transfer from cloth to polythene	Rod becomes −, cloth becomes +
Acetate rod rubbed with cloth	Electrons transfer from acetate to cloth	Rod becomes +, cloth becomes −
Balloon rubbed on hair	Electrons transfer from hair to balloon	Balloon becomes −, hair becomes +

Exam Tip: A very common exam mistake is saying that protons are transferred during charging by friction. This is wrong. Only electrons move. Protons are fixed in the nucleus and do not transfer between materials.

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Forces Between Charged Objects

The Rules

• Like charges repel: two positive objects repel each other; two negative objects repel each other.
• Opposite charges attract: a positive object and a negative object attract each other.

Charges	Force
+ and +	Repel
− and −	Repel
+ and −	Attract

Attraction of Charged and Uncharged Objects

A charged object can also attract an uncharged (neutral) object. This is because:

1. The charged object causes the charges in the neutral object to rearrange (this is called induction).
2. The opposite charges in the neutral object are drawn closer to the charged object, while the like charges are pushed further away.
3. Because the opposite charges are now closer, the attractive force is stronger than the repulsive force, resulting in a net attraction.

This explains why a charged balloon sticks to a neutral wall.

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Electric Fields

An electric field is the region around a charged object where another charged object experiences a force. (Electric fields are covered in more detail in the next lesson.)

Key points:

• Electric field lines point away from positive charges and towards negative charges.
• The strength of the field is greatest close to the charged object (where the field lines are closest together).
• A charged object placed in an electric field will experience a force.

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Sparking and Discharge

When a large enough charge builds up on an object, the potential difference between the charged object and its surroundings can become so great that the charge jumps across the gap as a spark.

How Sparking Occurs

1. A large amount of charge builds up on an object.
2. The potential difference between the object and a nearby conductor (or the ground) becomes very large.
3. The strong electric field ionises the air molecules between them.
4. This creates a conducting path through the air.
5. The charge flows rapidly through this path — this is the spark.

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Applications of Static Electricity

1. Electrostatic Precipitator (Removing Pollution)

Electrostatic precipitators are used in power stations and factories to remove dust and smoke particles from waste gases before they are released into the atmosphere.

How it works:

1. Waste gas (containing smoke/dust particles) passes between charged metal plates or grids.
2. The plates give the dust particles a negative charge.
3. The negatively charged dust particles are then attracted to positively charged collecting plates.
4. The dust sticks to the collecting plates and is periodically knocked off and collected.
5. The clean gas exits through the chimney.

2. Electrostatic Spray Painting

Static charge is used in spray painting to achieve an even coat of paint with less waste.

How it works:

1. The spray nozzle gives the paint droplets a charge (e.g. negative).
2. The object being painted is given the opposite charge (e.g. positive) or is earthed.
3. The charged paint droplets are attracted to the object.
4. The droplets spread out evenly because like charges repel each other — this prevents droplets from clumping together.
5. Paint even reaches the back of the object because the droplets are attracted around it.
6. Less paint is wasted because the droplets are attracted to the object rather than drifting away.

3. Photocopiers and Laser Printers

These use static charge to attract toner (fine powder) to a drum in the correct pattern, which is then transferred to paper and fixed with heat.

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Dangers of Static Electricity

1. Lightning

• Friction between ice crystals in clouds causes a massive build-up of static charge.
• The base of the cloud becomes negatively charged.
• This induces a positive charge on the ground below.
• When the potential difference is large enough, a huge spark (lightning bolt) jumps between the cloud and the ground.
• Lightning can cause fires, damage buildings, injure or kill people.

2. Sparks Near Flammable Substances

• Refuelling aircraft or vehicles: friction between the fuel and the pipe can build up static charge. A spark could ignite the fuel vapour, causing an explosion.

• Prevention: the fuel tanker and aircraft are connected by a bonding wire (earth strap) to ensure they are at the same potential, preventing charge build-up.

• Flour mills, grain silos, and operating theatres: static sparks can ignite dust, gases, or flammable anaesthetic gases.

• Prevention: equipment is earthed; anti-static materials are used; humidity is controlled.

3. Electric Shocks from Static