Tamil Nadu HSE+2 Physics Electrostatics Solutions: Questions & Answers

No.

Question

Answer

1

What is meant by quantisation of charge?

The charge on an object is an integral multiple of the elementary charge, given by q=neq=ne, where nn is an integer.

2

Which charge configuration produces a uniform electric field?

An infinite uniformly charged plane sheet produces a uniform electric field on either side.

3

Define electric field.

Electric field at a point is the force experienced by a unit positive test charge placed at that point: E=Fq0E=\frac{F}{q_0}.

4

Why do electric field lines never intersect?

At any point, the electric field has a unique direction. If field lines intersected, two directions would be assigned to the field at the same point.

5

What is an electric dipole?

An electric dipole consists of two equal and opposite charges separated by a small distance. Its dipole moment is p=q(2a)p=q(2a), directed from negative to positive charge.

6

Define electrostatic potential.

It is the work done per unit positive test charge in bringing the charge from infinity to a point in an electric field.

7

What is an equipotential surface?

A surface on which every point has the same electric potential is called an equipotential surface.

8

What is the relation between electric field and potential?

In one dimension, E=−dVdxE=-\frac{dV}{dx}. The electric field points in the direction of decreasing potential.

9

Define electric flux.

Electric flux through a surface is ΦE=E⃗⋅A⃗=EAcos⁡θ\Phi_E=\vec E\cdot\vec A=EA\cos\theta. Its SI unit is N m2C−1N\,m^2C^{-1}.

10

What is electrostatic shielding?

It is the protection of a region from external electric fields by enclosing it within a conductor.

11

What is polarisation in a dielectric?

Polarisation is the electric dipole moment per unit volume of a dielectric. In SI units, P=ϵ0χeEP=\epsilon_0\chi_eE.

12

What is dielectric strength?

It is the maximum electric field a dielectric can withstand without electrical breakdown.

13

Define capacitance and state its SI unit.

Capacitance is the ratio of charge to potential difference, C=QVC=\frac{Q}{V}. Its SI unit is farad (F).

14

What is corona discharge?

Corona discharge is the discharge of charge from a highly charged conductor, particularly around sharp points, due to ionisation of the surrounding air.

15

What happens to charge and capacitance when the applied voltage is doubled?

For a given capacitor, capacitance remains unchanged while charge doubles because Q=CVQ=CV.

Topic

Numerical Problem

Answer

Coulomb’s Law

Two charges 2 μC2\,\mu C and 3 μC3\,\mu C are placed 0.5 m0.5\,m apart in vacuum. Find the force between them.

0.216 N

Electric Field

Find the electric field at a point 0.2 m0.2\,m from a 4 μC4\,\mu C point charge.

9×105 NC−19\times10^5\,NC^{-1}

Electric Potential

Find the potential at a point 0.3 m0.3\,m from a 5 μC5\,\mu C charge.

1.5×105 V1.5\times10^5\,V

Electric Flux

An electric field of 500 NC−1500\,NC^{-1} passes normally through an area of 0.2 m20.2\,m^2. Find the flux.

100 Nm2C−1100\,Nm^2C^{-1}

Capacitance

A capacitor stores 6×10−6C6\times10^{-6}C at a potential difference of 12V12V. Find its capacitance.

0.5 μF0.5\,\mu F

Concept

Formula

Quantisation of Charge

q = ne

Coulomb’s Law

F = (1/4πε₀) × (q₁q₂/r²)

Electric Field

E = F/q₀

Electric Dipole Moment

p = q(2a)

Torque on a Dipole

τ = pE sin θ

Dipole Potential Energy

U = −pE cos θ

Electric Potential

V = W/q

Potential Due to a Point Charge

V = (1/4πε₀) × (q/r)

Electric Flux

Φₑ = EA cos θ

Gauss’s Law

Φₑ = Qₑₙcₗₒₛₑd/ε₀

Capacitance

C = Q/V

Parallel-Plate Capacitor

C = ε₀A/d

Capacitor with Dielectric

C = Kε₀A/d

Energy Stored in a Capacitor

U = ½CV² = Q²/(2C) = ½QV