Lesson focus: Static charging transfers electronA negatively charged particle with very little mass, found in shells around the nucleus of an atom. between insulating surfaces, producing charge imbalance and forces through an electric fieldThe area around a charged object where other charges feel a push or pull..
Use an electron-transfer model to explain attraction, repulsion, sparks and safe dischargeWhen built-up static charge flows away, sometimes as a spark..
Build on earlier learning
Forces at a distanceYear 7 introduced non-contact forces. This lesson explains electrostatic force using charge and fields.
Practical
Charging by friction
- Rub a polythene rod with a cloth and hold it near small paper pieces.
- Repeat with an acetate rod.
- Hang one charged rod and bring the other near: unlike charges attract, like charges repel.
Record: Observations for each pair of rods.
Charging by rubbing
Rubbing a balloon on a jumper moves electrons (negative charges) from the jumper to the balloon. The balloon becomes negative and the jumper positive. Like charges repel; opposite charges attract.
Controls
Only electrons move: the positive charges stay where they are. The second balloon was rubbed the same way.
You will be successful when you can…
- Describe charging by friction.
- Track electron transfer.
- Predict attraction and repulsion.
- Explain sparks and earthing safely.
Words that carry the science
- electric charge
- A property of matter that can be positive or negative and is measured in coulombs.
- electron
- A negatively charged subatomic particle that can transfer between materials.
- static electricity
- A charge imbalance that remains localised until it discharges.
- electric field
- A region in which an electric charge experiences a force.
- discharge
- Movement of charge that reduces a charge imbalance.
- earthing
- Providing a conducting path through which charge can flow to or from Earth.
Charging moves electrons, not positive nuclei
01Charging moves electrons, not positive nuclei
When two insulating materials are rubbed together, electronA negatively charged particle with very little mass, found in shells around the nucleus of an atom. may transfer because the materials hold electrons with different strengths. The object gaining electrons becomes negatively chargedHaving more electrons than protons, so it has a negative (−) electric charge.; the object losing electrons becomes positively chargedHaving lost some electrons, so it has a positive (+) electric charge..
The total charge of the isolated pair is conserved. Positive charge usually means an electron deficit, not that positive particles crossed between the objects.
02Fields produce forces without contact
Like charges repel and unlike charges attract. A charged object creates an electric fieldThe area around a charged object where other charges feel a push or pull. around it, so another charge placed in that region experiences a force.
A charged object can attract a neutral insulator by polarisationWhen the charges inside an uncharged object shift slightly because a charged object is nearby, so the two attract.: charges inside the neutral object shift slightly, leaving opposite charge closer and like charge farther away. The nearer attraction can be stronger.
03Discharge can be useful or hazardous
If the potential difference between charged objects becomes large enough, the electric fieldThe area around a charged object where other charges feel a push or pull. can ionise air and a spark transfers charge. Lightning is a much larger dischargeWhen built-up static charge flows away, sometimes as a spark.; fuel vapour can make a small spark dangerous.
earthingConnecting something to the ground with a wire so extra charge can flow away safely. provides a low-resistance conducting path so charge does not build up. Fuel tankers use bonding or earthing, while photocopiers and electrostatic paint spraying deliberately control charged particles.
Track charge after rubbing
A plastic rod gains 4 × 10⁹ electrons from a cloth.
- Electrons carry negative charge.
- The rod gains electrons, so it becomes negatively charged.
- The cloth loses the same number, so it becomes positively charged.
- The pair still has the same total charge as before; charge has been separated.
How to make the reasoning visible: State the transferred particle and show equal-and-opposite charge change.
Static-electricity investigation
Use the observations to explain each result; no high-voltage equipment is required.
| Trial | Objects | Observation | Best explanation |
|---|---|---|---|
| A | two rubbed plastic rods | repel | same sign of charge |
| B | rubbed plastic rod and cloth | attract | opposite net charges |
| C | charged rod near paper | paper lifts | polarisation of neutral paper |
| D | charged dome near earth wire | spark then no attraction | rapid discharge |
| E | uncharged rods | no consistent force | no detectable imbalance |
Why does trial C not prove the paper was already oppositely charged?
Why should humidity be controlled?
Check your understanding
Answer from memory, then check against the suggested answer.
Which particles usually transfer during static charging?
What happens between like charges?
What is earthing?
Why is a fuel tanker earthed before fuel transfer?
Explain how a charged balloon attracts a neutral wall.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A student rubs a plastic rod with a cloth. The rod becomes negatively charged. It then attracts small pieces of neutral paper.
Explain how the rod becomes negatively charged.
(4)Explain why the neutral paper is attracted to the rod.
(2)Total for this question: 6 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., trace electrons first, then use polarisation rather than claiming the paper already has net positive charge.