MODULE 3: ELECTRICITY AND MAGNETISM

Electrostatics

ElectrostaticsThe study of the effect that charges

in rest have on each other

Objects become

charged by gaining or

loosing electrons

Introduction

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- -++

++ -

-- -+

+

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Two types charges:

Positive:Shortage of Electrons

Negative:Excess of Electrons

Protons and neutrons cannot be

transferred!!!

IntroductionForces between charges:

Like charges repel each other

Opposite charges attract each other

Charging objectsFriction

Electrons are transferred when two objects are rubbed against each other

Charging objectsTouch

Electrons are transferred when a charged object touches a neutral object

Charging objectsInduction (polarization)

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Charged particles in a neutral object rearrange when a charged objects is

brought close to it

Causes temporary charge distribution so neutral object can be attracted

Charging objectsInduction (polarization)

Conservation of ChargeCharge cannot be created or

destroyed, but only transferred from one object to another.

Conservation of Charge

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++ -

-- -++

++

-

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-2 nC -4 nC

Charge distribute equally among both

spheres

Conservation of ChargeCalculate new charge on spheres

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++ -

-- -++

++

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-

-2 nC -4 nC

𝑄 𝑓=𝑄1+𝑄2

2

𝑄 𝑓=−2+(−4)

2𝑄 𝑓=−3𝑛𝐶

-3 nC-3 nC

Quantisation of ChargeNumber of electrons

∆𝑸=𝑸 𝒇−𝑸𝒊

𝒏𝒆=∆𝑸𝒒𝒆

Where = Charge Transferred(C)= Initial Charge (C) = Final Charge (C)= Number of Electrons= Charge of Electron= C

Example 1Two identical metal spheres have different charges. Sphere A has a charge of -5 nC.

Sphere B has a charge of 3 nC.

a) What is the nature of the force between A and B?

b) If the two spheres touched, what will the new charge on the spheres be?

c) What is the new nature of the forces between sphere A and sphere B?

d) In which directions were the electrons transferred?

e) How many electrons were transferred?

Example 2Two identical metal spheres have different

charges. Sphere A has a charge of –96 X 10-18 C. Sphere B has 60 excess

electrons.

a) What is the charge on sphere B?b) If the two spheres touched, what will

the new charge on the spheres be?c) How many electrons were transferred?