Most asked questions
5 min read

Electrostatic Potential And Capacitance

- Get to know usually which areas are frequently asked in the CBSE exam

Discuss and explain the relation between electric field intensity and potential

The relationship between electric field and scalar potential is given as:
, where gradient operator.

Potential due to a dipole at a general point

Potential due to a dipole is given by:

electric dipole moment
angle made by the line joining center of dipole and the point with the dipole moment vector
distance between the center of dipole and the point
Approximation is made that the length of dipole is negligible as compared to the distance of the point from the dipole.

Equipotential surfaces

Surfaces having same potential are termed as equipotential surfaces
The properties of equipotential surfaces can be summarized as follows:
  • The electric field lines are normal to the equipotentials and are directed from higher to lower potentials. 
  • By symmetry, the equipotential surfaces produced by a point charge form a family of concentric spheres, and for a constant electric field, a family of planes normal to the field lines. 
  • The tangential component of the electric field along the equipotential surface is zero, otherwise non-vanishing work would be done to move a charge from one point on the surface to the other.
  • Work done in moving a particle along an equipotential surface is zero. 

Capacitance of parallel plate capacitor

We know that
But and
putting these values in capacitance formula we get 
Where, A = Area of plate, d = Distance between capacitor plates

Capacitance of parallel plate capacitor with a combination of dielectrics

post image
In the figure shown, find the effective capacitance across P and Q. (Area of each plate is )
The above arrangement acts as the capacitor in parallel with and which are in series.

and are in series.

is in parallel with
Total capacitance

A parallel plate condenser is filled with two dielectrics as shown in figure. Area of each pate is and the separation is metre. The dielectric constants are and respectively. Its capacitance (in farad) will be :