Static ElectricityEdexcel IGCSE Physics: Revision notes
Section 1
Which materials conduct and which insulate?
Materials differ in how easily they allow charge to move through them:
- Electrical conductors (e.g. metals) allow charge to flow through them easily, because they contain free electrons that can move
- Electrical insulators (e.g. plastics) do not allow charge to flow through them easily, because their electrons are held tightly and cannot move freely
Static electricity builds up on insulators because charge cannot flow away/through them, whereas conductors allow charge to disperse.
Section 2
How does friction cause charging?
Rubbing two insulating materials together can transfer electrons from one to the other, leaving both objects charged. This can be investigated practically by rubbing insulating materials (e.g. a plastic rod with a cloth) and testing for the resulting charge.
- If electrons are transferred from an object, it is left with a positive charge (fewer electrons than protons)
- If electrons are transferred to an object, it is left with a negative charge (more electrons than protons)
Rubbing a polythene rod with a cloth transfers electrons from the cloth to the rod, leaving the rod negatively charged and the cloth positively charged.
Section 3
How are positive and negative charges produced?
Electrostatic charging always happens through the movement of electrons — protons do not move between materials.
- An object becomes positively charged when it loses electrons
- An object becomes negatively charged when it gains electrons
This explains all electrostatic phenomena: charge is never created or destroyed, only transferred from one object to another via electrons.
Do not describe charging as protons moving — in solids, only electrons are free to move; positive charge results from a loss of (negative) electrons, not a gain of protons.
Section 4
How do charges interact?
Charged objects exert forces on each other:
- Like charges repel — two positive charges, or two negative charges, push each other apart
- Unlike charges attract — a positive charge and a negative charge pull towards each other
These forces can be demonstrated by bringing two charged, freely-suspended objects near each other and observing whether they move together or apart.
Section 5
What are the dangers and uses of static electricity?
Dangers:
- When fuelling aircraft and tankers, friction between fuel and pipes can build up static charge; if this charge sparks, it can ignite fuel vapour, causing an explosion — bonding/earthing straps are used to prevent charge build-up
Uses:
- Photocopiers use static charge to attract toner (fine charged powder) onto a charged image of the document, which is then transferred and fused onto paper
- Inkjet printers use electrostatic deflection to control tiny charged droplets of ink, directing them precisely onto paper to form an image
When explaining dangers or uses, always link back to electron movement/charge build-up and the force of attraction/repulsion it creates — that is what the mark scheme rewards.
Must Know
- Conductors (e.g. metals) allow charge to flow; insulators (e.g. plastics) do not
- Rubbing insulating materials together transfers electrons, charging both objects
- Losing electrons → positive charge; gaining electrons → negative charge
- Like charges repel; unlike charges attract
- Danger: static charge can spark and ignite fuel vapour when fuelling aircraft/tankers
- Uses: photocopiers use charged toner; inkjet printers use charged ink droplets
That's the notes covered.
Carry on to the next subtopic.