Class 10 > Unit # 14: Electrostatics > Charging by Induction, Conduction & Friction

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Electrostatics - Electric Charge and Induction

Q. Describe Electric Charge. In how many ways can charge be produced in a body?

"Electric charge is a fundamental property of matter carried by elementary particles that governs how particles interact with electric and magnetic fields."

Charge is a scalar quantity, and its S.I. unit is the Coulomb (C).

Definitions of the Coulomb

1. In terms of elementary particles: One coulomb corresponds to the total charge of approximately $6.25 \times 10^{18}$ natural units of electric charge (such as electrons or protons), where a single electron has a charge of $-1.6 \times 10^{-19} \, \text{C}$.
2. In terms of electric current: According to the definition of the Ampere, "One coulomb is the amount of electric charge that passes through a cross-section of a conductor in 1 second when a steady current of 1 ampere flows through it."

Characteristics of Electric Charge

• Charge is an intrinsic property of matter determining mutual electrical attraction or repulsion.
• Friction between distinct materials (e.g., glass and plastic) produces two distinct types of charges.
• Like charges (same sign) repel each other.
• Unlike charges (opposite sign) attract each other.
• Repulsion is the only true and reliable test for determining whether a body is charged.

Methods of Charging a Body

There are three primary methods to impart electric charge to a body:

1. Induction:
   A method of charging a neutral body without making any physical contact with a charged object.
2. Conduction:
   A method of charging a neutral body by direct physical contact with a charged object.
3. Friction:
   Creating an imbalance of electrons and protons by rubbing two dissimilar objects against one another, transferring electrons via frictional contact.

Q. Define electrostatic induction. Explain charging by electrostatic induction.

"Electrostatic induction is the phenomenon of producing charge on a neutral body through the electrostatic influence of a nearby charged body, without any direct physical contact."

Figure: Step-by-step charging of metal spheres A and B via electrostatic induction.

Process of Charging by Electrostatic Induction

1. Initial Setup: Consider two neutral metal spheres, A and B, placed in contact with each other, supported on insulating stands.
2. Introduction of Charge: Bring a negatively charged object (such as a rubber balloon) close to sphere A without touching it.
3. Charge Redistribution: Due to electrostatic repulsion, the free electrons in the two-sphere system are repelled away from the balloon, migrating from sphere A across to sphere B.
4. Polarization: Consequently, sphere A acquires a net positive charge (due to a deficit of electrons), while sphere B acquires a net negative charge (due to an excess of electrons). The combined two-sphere system remains globally neutral.
5. Separation of Spheres: While the charged balloon remains in position, separate spheres A and B using insulating handles or gloves to prevent any charge leakage.
6. Final State: Remove the charged balloon. The charges redistribute evenly across each isolated sphere, leaving sphere A permanently positively charged and sphere B permanently negatively charged.

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