- Objects can be given one of two types of electric charge:
- When two charged objects are brought close together, there will be a force between those objects
Like charges repel; opposite charges attract
- Opposite charges attract
- Like charges repel
Whilst electrostatic forces share many similarities with magnetic forces, they are different phenomena – take care not to confuse the two!
- Electric charge is measured in units called coulombs (C)
- In your exam you will be expected to be able to explain how to give insulating materials a charge by the process of friction and to describe how to demonstrate the charging of materials in this way
- Suspend one of the insulating materials using a cradle and a length of string so that the material can rotate freely
- Rub one end of the material using a cloth (in order to give it a charge)
- Now take a second piece of insulating material and charge that by rubbing with a cloth
- Hold the charged end of the second piece close to the charged end of the first piece:
- If the first piece rotates away (is repelled) from the second piece then the materials have the same charge
- If the first piece moved towards (is attracted to) the second piece then they have opposite charges
Demonstrating Electric Charge
Experimental demonstrations, such as the one above, are different from experiments in which you have to take measurements.
When describing a demonstration you should state a conclusion – in other words, explain what you expect to happen and what it means.