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Electric Charge

Charge is the property associated with matter due to which it produces and experiences electrical and magnetic effects. The excess or deficiency of electrons in a body gives the concept of charge.

Types of charge :
(i) Positive charge : It is the deficiency of electrons as compared to proton
(i) Negative charge : It is the excess of electrons as compared to proton.

SI unit of charge : ampere × second i.e. Coulomb Dimension : [A T]

Practical units of charge are ampere × hour (=3600 C) and faraday (= 96500 C)

Millikan calculated quanta of charge by ‘Highest common factor’ (H.C.F.) method and it is equal to charge of electron.
• 1 C = 3×109 stat coulomb, 1 absolute – coulomb = 10 C, 1 faraday = 96500 C.

To have a better understanding about charge, do the following experiments.
(a) Rub a glass rod with silk and bring two such rods near each other. They repel each other.

(b) Now take a plastic rod instead of glass rod rub it with fur and repeat the above experiment. We find that they also repel each other.

(c) Now if we take a glass rod as (a) above and a plastic rod as (b) above and bring them near each other, we find that they attract each other.

We can conclude that a glass rod rubbed with silk produces one kind of charge and a plastic rod rubbed with fur creates another type of charge. Same type of charges repel each other and different type of charges attract each other. When the experiment is repeated we do not come across any other type of charge.

When bodies with opposite charges are brought into contact, charges disappear from both the bodies. This indicates that during rubbing one type of charge is transferred from one body to another. These get neutralised when the charged bodies are brought into contact.

Electric charge, like mass, is one of the fundamental attributes of the particle of which the matter is made. Charge is the physical property of certain fundamental particles (like electron, proton) by virtue of which they interact with the other similar fundamental particles. To distinguish the nature of interaction, charges are divided into two parts (i) positive (ii) negative. Like charges repel and unlike charges attract. SI unit of charge is coulomb and CGS unit is esu. 1 C = 3×109 esu.
Magnitude of the smallest known charge is e = 1.6 x 10-19 C (charge of one electron or proton).

To understand the nature and behaviour of charge fully, atomic structure is to be kept in mind. An atom consists of a nucleus (concentrated heavy portion in the centre) which comprises of positively charged particles protons and neutral particles neutrons. Negatively charged particles electrons revolve around nucleus. It is the transfer of these electrons which causes negative charge to pass from one body to another and in the process the first body gets positively charged.

Questions For You:

(i) When a glass rod is rubbed with silk it gets___________(positively / Negatively) charged. Why does the rod get this charge ?
(ii) Why is charge on an electron taken as the fundamental charge. Why can’t we take charge on a proton to be as fundamental charge?


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