Electric Charges: CBSE Physics Quick Revision Module 1

Contents:

Electric Charges, Conservation of Charge, Coulomb’s Law – force between two point charges, forces between multiple charges, superposition principle and continuous charge distribution.

Introduction

Electrostatics is the branch of Physics which deals with electric charges at rest and their properties.

When two suitable objects are rubbed against each other, charges appear on them. The electric charges acquired by them are immovable and they are called static charges and the electricity so produced is called static electricity. Since the charges are produced by rubbing or friction, the electricity so produced is also called frictional electricity.

Read history of electrostatics here



Origin of frictional electricity

Two kinds of charges

Charges are of two kinds; positive and negative. Initially when charges were discovered the two kinds of charges were called Rosie nose and vitreous. The charge acquired by Amber when rubbed with wool or fur The charge acquired by Amber was called resinous because Amber is formed from fossilised resin. The charge acquired by glass rod whenRubbed with silk is called vitreous. The term vitreous means glass like Missed chances will need to read named negative and positive by Benjamin Franklin. The charge acquired by Amber Is termed negative and the charge acquired by Glass is termed positive

Properties of charges

Like charges repel and unlike charges attract

repulsion is the sure test for charging

methods of charging

Charging by induction

charging by conduction

induction precedes attraction


Quantisation of charge (graininess or discreetness )

The charge present in any body is an integral multiple of the fundamental charge, the charge on an electron (1.6 x 10 -19 C)

Q = ne; Where n is an integer, positive or negative


quarks

Recent researches have established the existence of quarks which build up subatomic particles like protons and neutrons. The courts have fractional electronic charge like 1/3 e, 2/3 e etc. But this will not violate the quantisation of charge because first of all in our ordinary world Cox do not exist freely they always combine to form protons neutrons or other particles having integral multiple of electronic charges. Even if they are found to exist independently it only reduces the magnitude of the fundamental charge to the lowest of the charge on an independent quark.

law of conservation of charge
The law of conservation of charge states that charges can neither be created nor be destroyed in isolation. It is impossible to create a net positive charge or a net negative charge. Charges can be produced or destroyed only in equal and opposite Pairs

annihilation of matter and paint production

differences between mass and charge

Coulomb’s Law

mathematically

Coulomb’s law in vector form

Principle of superposition

continuous charge distribution

linear

planAr

Volumetric

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