‹‹ Previous | Formulae Page 1 | Next ››

1. Gauss's Theorem:

The total normal electric induction (TNEI) over a closed surface is equal to the algebraic sum of the electric charges enclosed by the surface.

T.N.E.I. =S Q_{1}

T.N.E.I. = K e_{0} Normal component of ´ surface area K = dielectrict constant of the medium e_{0} = Permitivitty of free space

2. Electric intensity at a point due to a charged sphere:

E =

q

4pk Î_{0} r^{2}

Or

s R^{2}

k Î_{0} r^{2}

=

s

kÎ_{0}

(

R

r

)

2

where

q : Total charge on the sphere R : radius of the spherical conductor r : distance of the point from the centre of the sphere s : surface density of charge or the sphere k : dielectric constant of the medium surrounding the sphere.

Remember: E =0 inside the charged sphere.

When point is very close to charged sphere

3. Electric intensity at a point just outside a long cylinder:

2pk Î_{0} r

s R

k Î_{0} r

where,

q : charge per unit length of cylindrical conductor R : radius of cross-section of cylindrical conductor r : distance of point from axis of cylinder s : surface density of charge on cylinder k : dielectric constant of the medium surrounding the cylinder.

4. Electric intensity at a point just outside a closed charged conductor:

k Î_{0}

where s : surface density of charge on the conductor.

5. Mechanical force per unit surface area of a charged conductor:

F

ds

s^{2}

2 Î

2k Î_{0}

1

kÎ_{0} E^{2}

E = magnitude of electric intensity at a point just outside the element. k = dielectric constant of the medium surrounding the conductor. s = surface density of charge on the conductor.

6. Energy density of a medium:

Energy per unit volume or Energy density of a medium in which electric field is present

dw =

Î_{0}k E^{2}

ke_{0}

k : dielectric constant of the medium E : magnitude of electric intensity in the region s = surface density of charge

7. Capacity of a conductor:

The capacity of a conductor is defined as the ratio of the charge on the conductor to the potential of the conductor

Capacity (C) =

Charge(Q)

Potential(V)

C =

Q

V

\ Q = CV

1 farad =

1 Coulomb

1 Volt

1 micro farad (mF) = 10^{-}^{6} farad (F) 1 Pico farad (pF) = 10^{-}^{12} farad (F)

8. Capacity of a parallel plate condenser:

Capacity of a parallel plate condenser with a medium of dielectric constant k,

AÎ_{o} k

d

C_{air} =

AÎ_{o}

A : area of each plate d : distance between the plates,

C = k C_{air}

9. Energy stored in a charged condenser:

U =

Q^{2}

2C

CV^{2}

QV

Q : magnitude of charge on each plate C : capacity of the condenser V : potential difference between the plates.

10. Equivalent capacity of number of condensers connected in series:

The equivalent capacity of a number of condensers (having capacities C_{1}, C_{2}, …, C_{n}) connected in series

C

C_{1}

+

C_{2}

+...+

C_{n}

or

11. Equivalent capacity of number of condensers connected in Parallel:

The equivalent capacity of a number of condensers (having capacities C_{1}, C_{2}, …, C_{n}) connected in parallel

C = C_{1} + C_{2} + … + C_{n} or C =