Electric Charge

Electric Charge is a fundamental property of matter and is never found free. There are two types of electric charges: positive and negative. If a body has an excess of electrons, it is said to be negatively charged, and if it is deficient in electrons, it is said to be positively charged.

Electric Charge: An Introduction

1. The concept of positive and negative charges was introduced by Benjamin Franklin.

2. The sure test for the detection of a charge is repulsion.

3. In S.I. system, the unit of charge is the Coulomb.

4. Electric charge is a scalar quantity.

5. Opposite charges attract and like charges repel.

6. Electric charge is conserved; it cannot be created or destroyed, only transferred between objects.

7. The charge is quantized, with the smallest charge associated with an electron (-) and proton (+) being $\times {10}^{-19}$ coulombs.

All charges in nature exist as integral multiples of the electron charge, where $q=n\cdot e$

A coulomb is equivalent to a charge of 6.24310¹⁸ electrons.

When a body is positively charged, its mass slightly decreases. When a body is negatively charged, its mass slightly increases.

Special Cases:

1. In the case of a conductor, its charge is spread over the entire outer surface, whereas in the case of an insulator, its charge is localized.

2. The electric charge given to a conductor always resides on the outer surface of the conductor.

Charging of Bodies

Electrification is the process of making a neutral body into a charged body, and is a universal phenomenon.

A body can be electrically charged by any of the following three ways:

• Friction
• Contact
• Electrostatic Induction

Charging by Friction

The electricity (i.e. transfer of electrons) that is produced due to friction is called frictional electricity.

Process of Charging

When two neutral bodies are rubbed together, there is a transfer of electrons from one body to the other due to structural modifications caused by the frictional forces acting on them.

In this method, one of the bodies acquires a negative charge while the other gets a positive charge, both of which are equal in magnitude.

Examples

When a glass rod is rubbed with a silk cloth, the glass rod acquires a positive charge and the silk cloth acquires a negative charge. Electrons are transferred from the glass rod to the silk cloth.

When a ebonite rod is rubbed with fur cloth, the ebonite rod acquires a negative charge and the fur cloth acquires a positive charge. Electrons are transferred from the fur cloth to the ebonite rod.

Electric Series

The substances mentioned below are referred to as the “Electric Series,” and they are arranged in a way such that if two of them are rubbed together, the one occurring earlier will be positively charged.

• Glass, Flannel, Wool, Silk, Sealing wax, Hard metal, Hard rubber, Resin, Sulphur, etc.

Explanation: When a glass rod is rubbed with silk, the glass will acquire a positive charge while silk will get a negative charge if glass and silk are selected.

Charging by Contact

A neutral body can gain a charge by coming in contact with a charged body. This will cause the neutral body to acquire the same charge as the charged body, resulting in both bodies having the same charge. This process also causes the electric charge on the first body to decrease.

Charging by Electrostatic Induction

Induction occurs when a charged body is brought near an uncharged body, resulting in the polarisation of charges in the uncharged body. This phenomenon always occurs before attraction.

The induced charge on a dielectric slab with dielectric constant K is given by $$q^1=-q\left[ 1-\frac{1}{K} \right].$$

Without a decrease in charge of the body induced by the method of induction, bodies can be continuously charged.

Related Topics

• Electrostatics
• Gauss’s Law
• Coulomb’s Law
• Electric Field Intensity
• Equipotential Surface
• Electric Potential Energy

Frequently Asked Questions on Electric Charge

What are the two types of charges?

• Answer: The two types of charges are positive charges and negative charges.

Positive and negative are the two types of charges.

What is the Charge Ratio of the Proton to the Electron?

• The charge of the proton is equal in magnitude to that of an electron, but opposite in charge.

Do Uncharged Bodies Attract Charged Particles?

• Yes, a charged particle will attract lighter uncharged bodies.

How Does Charging by Conduction Work?

• The process of charging a neutral conductor by bringing it into contact with a charged body is called ‘charging by conduction’.

How Does Charging by Induction Work?

• Charging a conductor without making contact with it by bringing a charged body close to it is called induction.