Static Electricity and Electric Fields — AQA GCSE Physics (Separate)
Static electricity is the build-up of charge on insulators, which creates electric fields and forces.
How charge builds up
When two insulating materials are rubbed together, electrons (which are negatively charged) are transferred from one material to the other:
- The material that gains electrons becomes negatively charged.
- The material that loses electrons becomes positively charged.
Only electrons move — protons stay in the nucleus. For example, rubbing a polythene rod with a cloth gives the rod a negative charge.
Forces between charges
- Like charges repel (two positives, or two negatives).
- Unlike charges attract (a positive and a negative). These are non-contact forces.
Sparks
A charged object can cause sparks. As charge builds up, the potential difference between the object and an earthed conductor increases. If it is large enough, electrons jump across the gap (through the air), causing a spark (e.g. static discharge from a doorknob).
Electric fields
A charged object creates an electric field around it. The field is strongest close to the object. A second charged object placed in the field feels a force. Field lines point away from a positive charge and towards a negative charge.
Exam tips
- Charging by friction transfers electrons (negative); the rest is left positive.
- Like charges repel, unlike attract (non-contact forces).
- Sparks happen when the p.d. is large enough for charge to jump across a gap.
- An electric field is strongest close to a charge; field lines show its direction.