Positive and Negative Charge

Introduction to positive and negative charge:

In 1600, a philosopher Gilbert observed that Amber and several other materials such as glass, ebonite, paper, etc. on being rubbed attract light bodies. This property is developed due to rubbing i.e. by friction. On acquiring this property material is said to be ‘electrified’. On being electrified, material is said to have acquired ‘charge’. Because the charge acquired by the material cannot flow from one point to another, this type of charge is called as ‘static charge’. When a glass rod is rubbed with silk, glass rod developed a positive charge. When an ebonite rod is rubbed with cat-skin, ebonite rod developed a negative charge.

Experiment shows that charges are of two types: 1. Positive charge 2. Negative charge. These names were given by Benjamin Franklin in 1750.

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Quantization of positive charge and negative charge :


Several experiments have shown that in nature positive charge and negative charge are found to be made up of integral multiples of a smallest amount of charge. This amount is 1.6 x 10^-19 coulomb. It is denoted by ‘e’ and is the charge of electron and proton. All the existing charges are found to be ‘ne’ or a multiple of ‘e’, here n is a integer (such as e, 2e, 3e, -e, -2e, -3e, -4e). No charge is found to be fraction of e such as 1.4e, 0.6e, 0.9e . That means electric charges can be divided indefinitely. This property of charge is called as quantization of charge.  Since e is smallest amount so it is called as elementary charge.

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Charges of elementary particles :


Electron has a negative charge(-e). Proton has a positive charge(+e). Alpha particles have two positive charges (+2e) while beta particles have a negative charge(-e).

Unit of positive and negative charge

In MKSA system, the unit of charge is coulomb and its symbol is ‘C’. it means that positive and negative charges are measured in coulomb such as -34 C , 50 C, 24 C, -55C etc.