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ELECTROSTATICS
Electrostatics
The branch of Physics which deals with electric effects of static charge is called electrostatics.
Electric Charge
Charge of a material body or particle is the property due to which it produces & experiences electrical & magnetic effects. Where do charges come from? In an atom, a positively charged nucleus is surrounded by electrons The protons (+) in the nucleus attract the electrons (-), while the electrons repel each other This attraction and repulsion behavior gives an object its charge
Where do charges come from?
Matter is made up of atoms. An atom consists of proton, neutron& electron. Proton = + ve charge Electron= - ve charge Neutron = no charge
Properties of charges Charge comes in two types, positive and negative; like charges repel and opposite charges attract.
CONSERVATION OF CHARGE
In an isolated system, sum of total charge remains constant whatever change takes place in that system.
QUANTIZATION OF CHARGE
Charge of a particle or a body is always an integral multiple of a fundamental unit of electric charge
- Charge is always associated with mass. Charge can’t exist without mass though mass can exist with charge.
- Charge is relativistic ally invariant. Charge is a scalar quantity. Its S.I. unit is Coulomb (C).
- A Charge at rest produces only electric field around itself.
- A charge moving with uniform velocity produces electric &magnetic field both.
- An accelerated charge emits electromagnetic radiations.
GROUNDING
An object is grounded when it is connected to the earth through a connecting wire. If a charged conductor is grounded, it will become neutral. One symbol that is often used to show that something is grounded is: How does grounding occur? When we touch a metal ball of positive charge...
- Electrons flow from the earth to the metal ball to neutralize the metal ball. Metal ball becomes neutral. + Similarly, if the metal ball is of negative charge...Extra electrons flow from the metal ball to the earth and the ball becomes neutral. METHODS OF CHARGING OF A BODY Primarily a body can be charged by six methods namely, (a) By friction (b) By Conduction (c) By Induction (d) By thermionic emission (e) By Photoelectric effect (f) By Field emission
CHARGING BY FRICTION
When insulators are rubbed together, one gives up electrons and becomes positively charged, while the other gains electrons and becomes negatively charged. Common examples of charging by friction:
- small shocks from a doorknob after walking on carpet with rubber-soled shoes laundry from the dryer that clings• balloon rubbed with hair sticks that to a wall.
CHARGING BY INDUCTION
(a) Bring a negatively charged rod near a neutral conducting sphere. Due to repulsion from rod free electrons of conducting sphere move away from rod. Thus a net positive charge appears near rod and negative charge away from rod. (b) Now connect the sphere to ground through a conducting wire from the side where negative charges appear. (c) Due to grounding the negative charges flow to the ground, leaving the sphere positively charged. (d) Now, remove the rod. The positive charges on the sphere arrange themselves uniformly.
Electroscope
Th The electroscope can be charged either by conduction or by induction. The charged electroscope can then be used to determine the sign of an unknown charge.
