AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Static charge
Electricity · Lesson 9 of 10
Warm-up
Answer each one, then check.
1. What charge do electrons have?
Negative
2. What is an insulator?
A material that does not conduct electricity
3. What is a non-contact force?
A force between objects that are not touching
4. What charge does a proton have?
Positive
5. Like charges...
Repel
Learning Objectives
1. Describe the production of static electricity by rubbing.
2. Explain charging in terms of the transfer of electrons.
3. Describe evidence that charged objects exert non-contact forces.
4. Explain sparking.
Static Electricity
When insulating materials are rubbed together, electrons are transferred: the material that gains electrons becomes negatively charged and the one that loses them is left with an equal positive charge.
Objects with the same type of charge repel; objects with different types of charge attract.
Charging by Rubbing
|
Only electrons move; protons stay in the nuclei. |
A polythene rod rubbed with a cloth gaining electrons, and pairs of charged balls attracting or repelling.
Explaining Charging
|
Explain why a polythene rod becomes negatively charged when rubbed with a cloth. |
1. Friction
Rubbing transfers energy so electrons can move
2. Electrons move
Negatively charged electrons are rubbed off the cloth and on to the rod
3. The rod
Gains electrons, so it becomes negatively charged
4. The cloth
Loses electrons and is left with an equal positive charge
Answer: Electrons transfer from the cloth to the rod; the rod becomes negative and the cloth positive.
Sparking
|
Explain how a spark can jump from a charged object to an earthed conductor. |
1. Charge builds
A large amount of charge collects on the object
2. Strong field
The electric field between the object and the conductor becomes very strong
3. Air ionises
The air becomes ionised and conducts, so charge flows as a spark
Answer: Charge builds up until the field is strong enough to make air conduct, and the charge flows as a spark.
Evidence of Non-Contact Forces
|
Repulsion Two charged rods of the same charge push each other apart. |
Attraction A charged rod attracts small pieces of paper or a stream of water. |
|
Hanging balls Suspended charged balls move apart or together without touching. |
Balloon on a wall A rubbed balloon can stick to a wall. |
Common Mistakes
Be precise.
▸ Only electrons move. Positive charges (protons) are fixed in the nucleus and do not move when rubbed.
▸ Insulators. Only insulators keep the charge; a metal rod held in the hand loses its charge.
▸ Say gained or lost. Say 'gained electrons', not 'gained negative charge'.
Key Terms
|
Static electricity Charge that builds up on an insulator. |
Electron A negatively charged particle. |
|
Non-contact force A force between objects that are not touching. |
Earthing Connecting to the ground so charge can flow away. |
|
Repel Push apart. |
Attract Pull together. |
Your Task: Rub and Predict
10 minutes
|
A student rubs a cloth on a balloon. The balloon is then attracted to the wall. Explain what has happened to the electrons and what type of charge the balloon has. 1. Say which way electrons moved. 2. State the charge on each object. |
A good answer shows: Electrons are transferred from the cloth to the balloon. The balloon gains electrons and becomes negatively charged; it attracts the wall.
Can I...?
☐ Explain how rubbing makes charge.
☐ Say which particles move.
☐ State the charge on each object.
☐ Describe attraction and repulsion.
☐ Describe evidence for non-contact forces.
☐ Explain sparking.
☐ Explain why insulators keep charge.
☐ Use the terms gained and lost electrons.
Summary
✓ Rubbing insulators transfers electrons.
✓ The material that gains electrons is negative; the one that loses electrons is positive.
✓ Like charges repel, unlike attract.
✓ Sparks occur when the field is strong enough to ionise air.
|
EXAM FOCUS Explain how a polythene rod becomes negatively charged when rubbed with a cloth. (3 marks) Say which way the electrons move. |