Revision notes for Edexcel GCSE Physics Charging by friction and electrostatic phenomena. Open the guide for explanations and worked examples. Written against the Edexcel GCSE Physics (1PH0) specification, so the content matches what's examinable rather than general Physics background.
Charging by friction and electrostatic phenomena
What you'll learn
- How an insulator can become charged when it is rubbed.
- Why gaining electrons makes an object negative, while losing electrons makes it positive.
- How static charges explain shocks, lightning, charged balloons, and charged combs.
- How electrostatic charges are useful — and why sparking can be dangerous.
These Edexcel 1PH0 points are marked with “P”, so they are Separate GCSE Physics content.
The starting point: atoms and charge
Matter is made of atoms. Inside atoms are protons, which have positive charge, and electrons, which have negative charge. In solids, the protons are fixed inside the atoms, but electrons can sometimes be transferred between materials.
A neutral object has equal amounts of positive and negative charge overall. It is not “empty of charge” — the positive and negative charges just balance.
Definition
Electric charge
Electric charge is a property of particles and objects that can cause forces. There are two types of charge: positive charge and negative charge.
Static electricity
Static electricity is the build-up of electric charge on an object. “Static” means the charge is not flowing continuously around a circuit.
This often happens on insulators.
Definition
Insulator
An insulator is a material that does not allow electrons to move through it easily. Plastic, rubber, glass, dry hair, and many fabrics are common examples.
Because electrons cannot move freely through an insulator, any charge that builds up tends to stay in one place for a while.
Charging an insulator by friction
When two insulating materials are rubbed together, friction can transfer electrons from one material to the other. The protons do not transfer.
For example, if a plastic rod is rubbed with a cloth, electrons may move from the cloth to the rod. The rod now has more electrons than protons, so it becomes negatively charged. The cloth has lost electrons, so it is left positively charged.
Key Idea
Only electrons move
In GCSE static electricity explanations, charge transfer happens because electrons move. A material that gains electrons becomes negative; a material that loses electrons becomes positive.
If the two materials were neutral before rubbing, the amount of negative charge gained by one material is equal to the amount of positive charge left on the other. Charge has not been created from nothing — it has been transferred.
Example
Deciding the final charges after rubbing
A dry plastic rod is rubbed with a cloth. Electrons transfer from the cloth to the rod.
- The moving particles are electrons, so the cloth loses negative charge and the rod gains negative charge.
- The rod now has more electrons than protons, so the rod is negatively charged.
- The cloth now has fewer electrons than protons, so the cloth is positively charged.
- The electrons lost by the cloth are the same electrons gained by the rod, so the charges are equal in size and opposite in sign.
Common Mistake
Positive charge does not mean extra protons
At GCSE, an object becomes positively charged because it has lost electrons, not because protons have moved onto it.
Forces between charged objects
Charged objects exert electrostatic forces on each other. These forces can act without the objects touching.
You need to remember the charge rules:
- Like charges repel.
- Unlike charges attract.
So two negative objects repel each other. Two positive objects also repel each other. A positive object and a negative object attract each other.
Key Idea
Charge force rule
Like charges repel; unlike charges attract.
This rule explains why charged objects can move, stick, separate, or suddenly discharge.
Attraction by induction
A charged object can attract a neutral object. This may feel surprising, because neutral objects have no overall charge.
The key idea is induction.
Definition
Induction
Induction is the rearrangement of charges in an object caused by a nearby charged object, without contact.
Suppose a negatively charged balloon is brought near a neutral wall. The electrons in the wall are repelled slightly away from the balloon. This leaves the surface closest to the balloon slightly positive. The balloon is then attracted to that nearby positive surface.
The wall is still neutral overall — its charges have just shifted slightly.
This also explains how a charged comb can pick up small pieces of paper. The charged comb causes electrons in the paper to shift, making the side nearest the comb oppositely charged.
Example
Explaining why a charged balloon sticks to a wall
A balloon has become negatively charged after being rubbed on hair. It is held near a neutral wall.
- The balloon has excess electrons, so it repels electrons in the wall away from the surface nearest the balloon.
- The near surface of the wall is left slightly positive, while the far side becomes slightly negative. The wall is still neutral overall.
- The negative balloon is closer to the slightly positive surface than to the slightly negative far side, so the attraction is stronger than the repulsion.
- There is a resultant attractive force, so the balloon can stick to the wall.
Common Mistake
Neutral objects can still be attracted
Do not write “the wall is neutral, so there is no force”. A neutral object can be attracted if its charges are rearranged by induction.
Everyday shocks and sparks
If charge builds up on your body, it may suddenly move when you touch a conductor such as a metal door handle. This sudden movement of electrons is an electrostatic discharge. You may feel it as a small shock.
This can happen after walking across a synthetic carpet, removing a jumper, or sliding out of a car seat. Friction transfers electrons, so your body and the other material become charged.
A spark happens when charge jumps through air. Air is normally an insulator, but if the charge build-up is large enough, electrons can move through it suddenly.
Lightning is a huge electrostatic discharge. Inside storm clouds, collisions between water droplets and ice particles separate charge. When the charge build-up becomes large enough, electrons move rapidly through the air between clouds or between a cloud and the ground. That discharge is lightning.
Earthing
Earthing means connecting a charged object to the Earth using a conductor. The Earth is so large that it can accept or supply electrons without becoming noticeably charged.
Definition
Earthing
Earthing is the removal of excess charge by allowing electrons to move between an object and the Earth.
The direction of electron movement depends on the charge:
- If an object is negatively charged, it has excess electrons. Electrons flow from the object to Earth.
- If an object is positively charged, it has lost electrons. Electrons flow from Earth to the object.
Either way, earthing reduces the charge imbalance.
Example
Choosing the electron flow during earthing
A metal fuel tanker has built up excess negative charge and is connected to Earth by a metal wire.
- Excess negative charge means the tanker has too many electrons.
- The metal wire provides a conducting path, so electrons can move away from the tanker.
- Electrons flow from the tanker to Earth, reducing the charge on the tanker.
- With less charge build-up, there is a smaller risk of a spark jumping to nearby objects.
Tip
Describe earthing using electrons
For full marks, say which way electrons move. Avoid vague answers like “the electricity goes into the ground”.
Dangers of electrostatic sparking
Sparks are not just annoying — they can be dangerous if flammable gases or vapours are nearby.
When fuelling cars, petrol vapour can form around the fuel nozzle. Charge may build up due to friction as fuel flows through pipes or as people move against clothing and seats. If a spark occurs near petrol vapour, it could ignite the vapour and cause a fire or explosion.
Earthing helps prevent this. Fuel tankers, aircraft, and pipes are often earthed or bonded together so charge does not build up enough to cause a spark.
Common Mistake
Sparks need a large charge build-up
Air usually acts as an insulator. A spark happens only when the charge build-up is large enough for electrons to jump through the air gap.
Useful electrostatic charges
Static electricity is not always a problem. It can be useful when we want charged particles or droplets to move in controlled ways.
Insecticide sprayers
In insecticide sprayers, the tiny liquid droplets are given the same type of charge as they leave the nozzle. Because like charges repel, the droplets spread out into a fine, even spray.
The crop or plant may be earthed or oppositely charged. This means the droplets are attracted to the plant, giving better coverage and reducing waste.
Example
Explaining an electrostatic insecticide sprayer
An insecticide sprayer gives each droplet the same negative charge.
- The droplets all have like charges, so they repel each other and spread out instead of clumping together.
- The charged droplets form a fine mist, which can cover a larger area more evenly.
- If the plant is earthed or becomes oppositely charged by induction, the droplets are attracted towards it.
- More insecticide lands on the plant, so less spray is wasted in the air or on the ground.
Other uses of electrostatic charge include electrostatic paint spraying and some printing processes, where charged particles are attracted to particular surfaces.
The explanation pattern to learn
Most static electricity questions can be answered using the same chain of ideas:
- Friction or contact transfers electrons, or a nearby charge rearranges electrons by induction.
- Gaining electrons makes an object negative; losing electrons makes it positive.
- Like charges repel and unlike charges attract.
- If charge builds up, a spark may occur; earthing allows electrons to move safely and reduce the charge.
Exam technique
In the exam
- Always explain charging in terms of electron transfer, not movement of protons.
- For attraction by induction, state that the neutral object remains neutral overall but its charges are rearranged.
- For dangers, link the spark to a flammable vapour or gas, then explain that earthing prevents charge build-up by electron movement.
Self review
Check yourself
- If a cloth loses electrons while rubbing a rod, what charge does the cloth have afterwards?
- Why can a negatively charged balloon attract a neutral wall?
- How does earthing reduce the risk of a spark when fuelling a vehicle?
Recap questions
Test yourself with 5 quick questions on this guide. Answer them all correctly to complete it.
You've reached the end
Test yourself on this topic, or move on to the next guide.
How was this guide?