Key Stage 3 science · Physics – Electricity and electromagnetism

KS3 static electricity and electric fields: a parent’s guide

Key Stage 3 pupils explain static electricity properly for the first time: when two insulating objects are rubbed together, electrons move from one to the other, leaving one negatively charged and the other positively charged. They learn the rules for the forces between charges, why a charged balloon sticks to a wall, and the idea of an electric field, the region where charges feel forces without touching.

Static electricity and electric fields, explained

Everything is made of atoms, and atoms contain positively charged protons in the nucleus and negatively charged electrons around it. Usually the numbers are equal, so an object has no overall charge. When two different insulating materials are rubbed together, some electrons are rubbed off the surface of one and on to the other. The material that gains electrons becomes negatively charged, and the one that loses them becomes positively charged by exactly the same amount. The protons do not move. Rubbing does not create charge: it separates charge that was already there.

Charged objects exert forces on each other. Like charges repel and opposite charges attract. Two balloons rubbed with the same cloth push apart, and a balloon and the cloth pull together. The force gets stronger when there is more charge and when the objects are closer. A charged object can also attract an uncharged one, such as a charged comb picking up scraps of paper. The charges in the neutral object shift slightly, so the side nearest the comb ends up with the opposite charge. That nearer charge is attracted more strongly than the far charge is repelled, giving a small net pull.

Charge stays on insulators because the electrons cannot move away easily, but it leaks away gradually. Damp air carries charge off quickly, which is why static is more noticeable on dry winter days. If enough charge builds up, it can jump across a gap as a spark. A shock from a door handle after walking on a nylon carpet, and lightning on a very large scale, are both examples. Static charge can also be dangerous: tankers and aircraft are connected to the ground when refuelling so that sparks cannot ignite fuel vapour. Schools often mention photocopiers or paint sprayers as examples of useful static.

The idea of an electric field explains how a force can act across a gap. An electric field is the region around a charged object in which another charge feels a force without any contact, even through air or a vacuum. It is drawn with field lines and arrows showing the direction a small positive charge would be pushed: away from a positive charge and towards a negative one. Lines are closer together where the field is stronger. Pupils may see this when a volunteer’s hair stands on end while they touch a large charged metal dome, or when a stream of water bends towards a charged rod.

Words your child will hear

Electron: A tiny negatively charged particle. In solids it is electrons that move when objects become charged.
Insulator: A material that does not let charge flow easily, so it can hold static charge.
Positive and negative charge: An object with extra electrons is negative. One that has lost electrons is positive.
Repel and attract: Like charges push apart (repel) and opposite charges pull together (attract).
Electric field: The region around a charged object where another charge feels a force without touching.
Field line: A line with an arrow in a diagram showing the direction of the force on a positive charge.
Discharge: The loss of built-up charge, often with a spark.

What the National Curriculum says

The programme of study for Key Stage 3 says:

Pupils should be taught about separation of positive or negative charges when objects are rubbed together: transfer of electrons, forces between charged objects
Pupils should be taught about the idea of electric field, forces acting across the space between objects not in contact

Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.

A worked example

A balloon is rubbed on a woolly jumper and then sticks to a wall. Explain what has happened in terms of electrons.

Before rubbing, the balloon, the jumper and the wall all have equal numbers of positive and negative charges, so each is neutral.
Rubbing transfers electrons from the jumper to the balloon. The balloon gains electrons, so it has an overall negative charge. The jumper has lost the same number, so it is positively charged. The protons have not moved.
Bring the balloon close to the wall. The wall is an insulator, but the electrons in its surface atoms are pushed slightly away from the negative balloon, leaving the wall’s surface nearest the balloon slightly positive.
Opposite charges attract. The positive surface charges are closer to the balloon than the negative ones, so the attraction is slightly stronger than the repulsion, and there is an overall force towards the wall.
The balloon stays there until the charge leaks into the air. Rubber is a good insulator, so this may take a while, though it happens sooner on a humid day.

Rubbing transfers electrons to the balloon, making it negative. It attracts the neutral wall, whose surface charges shift so the nearest part is positive, and the net force holds the balloon in place.

Common mistakes and how to help

Thinking rubbing creates electric charge

Charge seems to appear from nowhere when you rub a balloon on your hair.

What helps: Charge is moved, not made. The balloon gains exactly as much negative charge as the hair loses, so the total charge stays the same. Show that the cloth is charged oppositely.

Believing that positive charges move when an object becomes positively charged

“Positive” sounds like something has been added, so children imagine positive particles arriving.

What helps: In solids only electrons are free to move. An object becomes positive by losing electrons. Say it as “negative charge was taken away”, which leaves more positive charge than negative.

Thinking a charged object can only attract an oppositely charged one

The rule “opposites attract” is learned first and applied too strictly.

What helps: A charged balloon picks up uncharged paper and sticks to a neutral wall. The charges in the neutral object are rearranged. Only repulsion proves an object is charged.

Treating static electricity and current electricity as unrelated

They are taught in different lessons and show up differently in life, so they seem like two kinds of electricity.

What helps: It is the same charge in both cases. In static electricity the charge builds up and stays still, and in a circuit it keeps moving round. A spark is the moment static charge starts to flow.

How to help at home

Balloon tests. Rub a balloon on hair, wool, and a plastic bag in turn, and see which makes it stick to the wall longest. Try it on a dry day and after a hot shower in a steamy bathroom. Talk about why the results differ.
Two hanging balloons. Hang two balloons from thread. Rub them both with the same cloth and bring them near each other, and see them push apart. Then rub only one and watch what happens. This shows repulsion and attraction clearly.
Bend the water. Run a very thin stream of water from a tap and hold a rubbed balloon or plastic comb close to it, with no electrical equipment nearby. The stream bends towards it. Do this with an adult in the room, over a sink.
Picking things up. See what a charged comb or plastic ruler can lift: tiny scraps of tissue paper, puffed rice cereal, salt. Ask your child why even uncharged objects are attracted.
Spot the sparks. Notice clothes clinging after the dryer, crackling when a jumper comes off, and shocks from car doors or door handles. Ask your child to explain each in terms of electrons moving between surfaces.

Builds on

Year 6: Circuit components and symbols

Leads on to

Key Stage 4: Current, resistance, charge and circuits
Key Stage 4: Mains electricity and power
Key Stage 4: Magnetic fields and transformers