Electrostatics.

Question 1

What is charge q in terms of number of electrons e ?

Answer 1

q=ne

Question 2

Coulumbs Law

Answer 2

F= k q1q2/ r^. 
k=1/4πε₀
unit of k = N metre square per coulomb square
k= 9 x 10^9
ε₀= 8 x 10^-12

Question 3

Unit of k in electrostatics Coulomb’s law

Answer 3

N m^ c^-2

Question 4

Unit of ε₀ (permittivity of free space )

Answer 4

C^/N m^-2

Question 5

Field strength due to a point charge

Answer 5

E= k q/r^

Question 6

Direction of field strength due to positive and negative charge ?

Answer 6

Due to positive charge field strength is away from the charge and due to negative charge field strength is towards the charge.

Question 7

Electric potential V due to point charge

Answer 7

V= k q/r

Question 8

Electrostatic potential energy U of two point charges.

Answer 8

U= k q1q2/r

Question 9

What is electrostatic potential energy in terms of charge and electrostatic potential ?

Answer 9

U= qV

Question 10

Potential difference in an uniform electric field?

Answer 10

In an indoors electric field , potential difference V= Ed

Question 11

Formula of electric dipole

Answer 11

p=q(2a). Direction of p vector is from -q to +q

Question 12

Electric field strength E for a uniformly charged spherical shell

Answer 12

E(i)=0
E(s)=k q/R^= σ/ε₀
Eo= kq/r^

Question 13

Electric field strength e for a solid sphere of charge.

Answer 13

E(i)=Kqr/R³
E(s)=Kq/R^
Eo=Kq/r^

Question 14

Electric field strength E on the axis of a uniformly charged ring

Answer 14

E= Kqx÷(R²+x²)^3/2

At centre , x= 0 and hence E=0

Question 15

Electric field Strength E for a infinitely long line charge

Answer 15

E= λ/2πε₀r

Question 16

Electric potential V for a uniformly charged spherical shell

Answer 16

V(i) = V(s) = Kq/R=σR/ε₀

Vo=Kq/r

Question 17

Electric Potential for a solid sphere of charge

Answer 17

V(i)= Kq÷R³(1.5 R² - 0.5 r²)
V(s)=Kq/R
Vo=Kq/r

Question 18

Electric potential on the axis of a uniformly charged ring

Answer 18

V=Kq÷√R²+x²
At centre ,
x=0
V= Kq/R

Question 19

Electric Potential V for an infinitely long line charge

Answer 19

PD= λ÷2πε₀ ln (r₂/r₁)

Question 20

Torque due to an electric dipole when placed in an uniform electric field

Answer 20

Torque = pE sin #

Question 21

Electric potential energy U due to an electric dipole when placed in a uniform electric field

Answer 21

U=-PE= -pE cos#

Question 22

When an electric dipole is placed in an uniform electric field , what happens when #=0?

Answer 22

In #=0 , it’s a stable equilibrium position.
In this position , F=0
Torque =0
U=-p.E= minimum

Question 23

When an electric dipole is placed in an uniform electric field , what happens when #=180?

Answer 23

=0 is unstable equilibrium position. In this F=0 and torque = 0 but U= +p.E= maximum.

Question 24

Electric flux on surface formula ?

Answer 24

∫∞=∫E . dS

Question 25

Mathematically , what is Gauss Law?

Answer 25

∫E . dS= q(in) / ε₀

or ‘Electric Flux from a closed surface’= q(in) / ε₀

Question 26

Electric filed due to a plane sheet of charge

Answer 26

E=σ/2 ε₀

Question 27

What is electric field on the surface of any charged conducting body ?

Answer 27

E=σ/ε₀

Question 28

Electric filed of a conductor under electrostatic conditions?

Answer 28

E(i)= 0
E(s) = σ/ε₀

Question 29

What are the two properties of a conductor regarding electric field lines and electric potential.

Answer 29

1. On the surface of charged conductor electric lines are perpendicular to the surface
2. The potential of charged conductor through out its volume is same.

Question 30

Potential difference between two charged spherical shells

Answer 30

V1-V2=q1÷4πε₀(1/r1-1/r2)

Question 31

What is charge per unit length λ?

Answer 31

It’s charge distribution along a line.

dq = λ dx

Question 32

What is charge per unit area σ?

Answer 32

It’s charge distribution on the surface.

dq= σ dA

Question 33

What is charge per unit volume p?

Answer 33

It’s charge distribution throughout a volume.

dq= p dV