Static electricity (AQA GCSE Physics): Revision Notes
📚Revision Notes
Static electricity
What is static electricity?
Static electricity happens when electric charges build up on the surface of materials called insulators. These charges can be positive or negative.
When you rub two insulators together, friction causes electrons to move from one material to the other. This leaves one object with extra electrons (negative charge) and the other with fewer electrons (positive charge).
Note
Static electricity is different from current electricity because the charges stay in one place rather than flowing through a circuit. This is why we call it "static" - meaning stationary or not moving.
How objects become negatively charged
An insulator becomes negatively charged when electrons move onto it from another material.
Example
Worked Example: Polythene Rod
When you rub a polythene rod with a cloth:
Step 1: Electrons transfer from the cloth to the rod through friction Step 2: The rod gains extra electrons, so it becomes negatively charged Step 3: The cloth loses electrons, so it becomes positively charged Step 4: The charges are equal in size but opposite in type
How objects become positively charged
An insulator becomes positively charged when electrons move off it onto another material.
Example
Worked Example: Acetate Rod
When you rub an acetate rod with a cloth:
Step 1: Electrons transfer from the rod to the cloth through friction
Step 2: The rod loses electrons, so it becomes positively charged
Step 3: The cloth gains electrons, so it becomes negatively charged
Step 4: Again, the charges are equal in size but opposite in type
Important rule about electrons
Important
It is always electrons that move when objects become charged by friction. Electrons are much lighter than protons, so they can move easily between materials.
Protons stay in the nucleus of atoms and never move during static electricity.
This is a fundamental principle because electrons are located in the outer shells of atoms where they can be transferred, while protons are tightly bound in the nucleus.
Forces between charged objects
Charged objects create forces on each other according to two fundamental rules:
- Like charges repel - two positive charges push apart, two negative charges push apart
- Opposite charges attract - a positive charge and negative charge pull together
The closer the objects are, the stronger the force between them. This relationship follows an inverse square law - doubling the distance reduces the force to one-quarter of its original strength.
Note
These forces can be observed in everyday situations, such as when your hair stands up after going down a plastic slide, or when a balloon sticks to a wall after being rubbed on your clothing.
Common examples
Understanding these common examples helps demonstrate the principles in action:
Polythene rod:
- Becomes negative when rubbed with cloth
- Attracts positive charges
- Repels other negative charges
Acetate rod:
- Becomes positive when rubbed with cloth
- Attracts negative charges
- Repels other positive charges
These materials consistently behave the same way because of their different abilities to hold onto electrons during the friction process.
Key takeaways
Summary
Key Points to Remember:
- Static electricity is caused by electrons moving between insulators during friction
- Only electrons move - never protons
- Objects with the same charge repel each other
- Objects with opposite charges attract each other
- The charges created are always equal in size but opposite in type