## Electrostatic Potential And Capacitance

- Are you feeling tough? Let make it extremely simple
1
Potential energy of a system of two charges in an external field:

The potential energy of a system in an external field is the total work done in assembling the configuration in presence of the external field. It can be calculated easily in two steps:
• Potential energy of the system = U
• Potential energy of each individual charge under the external field=
So P.E. of a system of charges in an external field=
P.E. of the System (U)+Sum of (Potential Energy of Each Charge in presence of External Field)

U can be calculated for any number charges using the below formulae:
This video will further explain the method of calculating P.E. of a system of charges in an external field.
POTENTIAL ENERGY IN AN EXTERNAL FIELD
4 mins
2
Effect of Dielectric on Capacitance:
Whenever a dielectric is introduced between a parallel plate capacitor, its surfaces close to the positive and negative plates get polarised with opposite charge. If the surface charge density without the dielectric slab is , then due to the polarisation, the surface charge is effectively
The net electric field inside the dielectric and hence the potential difference between the plates is thus reduced. Consequently, the capacitance C increases from its value when there is no medium (vacuum).
So let's see how this reduced surface charge density affects the overall capacitance of the system.
EFFECT OF DIELECTRIC ON CAPACITANCE
5 mins
3
Energy Stored by Capacitors:
A capacitor is not achieved by magic. An external agent has to do some work in order to build up charge on the two plates of the capacitor. In transferring positive charge from positive conductor to negative conductor, work will be done externally, since at any stage positive conductor is at a higher potential than negative conductor. Total work done in charging the capacitor may be viewed as stored in the energy of electric field between the plates.
Energy Stored by Capacitors
6 mins