- A glass rod rubbed with a piece of silk brought close to a suspended glass rod rubbed with silk repels.
- Two pieces of silk cloth with which the glass rods were rubbed also repel each other.
- Two ebonite/ amber rods rubbed with cat’s fur repelled each other.
- An ebonite rod rubbed with cat’s fur attracted a glass rod rubbed with a piece of silk.
- When a glass rod rubbed with a piece of silk is made to touch two small pith balls (or polystyrene balls) suspended by silk/nylon threads, the balls repel each other.
- Similarly, when an ebonite/amber rod rubbed with cat’s fur is made to touch two small pitch balls suspended by silk/nylon threads, the balls repel each other.
- However, a pith balls (or polystyrene balls) touched with charged glass rod attracts another.
A careful analysis of these facts observed leads us to the following conclusion:
- The bodies like glass rods, ebonite/amber rods, silk fur etc. acquire electric charge on rubbing.
- The pith balls or polystyrene balls acquire electric charge by actual contact with a charge body.
- The charge developed on glass rod rubbed with silk is different from the charge developed on ebonite rod rubbed with fur. This is because a charged glass rod repels another charged glass rod, but attracts a charged ebonite rod; hence, there are two kind of charged. When a glass rod os rubbed with silk, the rod acquires one kind of charge and the silk acquires second kind of charge.
Benjamin franklin named the two kinds of charges as positive and negative. By convention, charge acquired by glass rod or cat’s fur is called positive. And the charge acquired by ebonite/amber rods or silk cloth is called negative.
There are two kinds of charges. The property which differentiates the two kinds of charges is called the polarity of charges.
If a body possesses an electric charge, it is said to be charged or electrified. When it has no charge, it is said to be neutral.