Grade 12 Chapter 2 : Electrostatic Potential and Capacitance

 Chapter 2: Electrostatic Potential and Capacitance. 

Starting from the concept of electrical work, we establish the concept of electrostatic potential energy. This energy per unit charge is defined as the electric potential. We obtain an expression for the potential of a source charge by bringing a unit test charge from infinity to a location in the space. Similarly, using the geometry, we can find the potential due to the dipole. 

Moreover, we can relate the electric field and the potential also. Usually, the electric field is taken as the negative of the potential gradient. 

To create a system of charges, we have to spend some energy and this will be stored as the potential energy of the system. The same logic can be extended for rotating a dipole in an external field. Here also, by doing work against the net torque of the uniform external field, we can store the energy in the dipole. 

A very interesting point of discussion in Chapter 2 is related to the electrostatics of the conductor. Accordingly, the electric field inside of a conductor is always zero due to polarization which rearranges the charges on the surface of the conductor. Similarly, to maintain the static condition, the external field must always be perpendicular to the surface. If there is a tangential component of the external field, then the charge will flow on the surface and the static condition is not maintained. Similarly, due to E being zero inside, there must be no charge inside the conductor. Using the relation of the electric field and the potential gradient, we can show that the potential inside a conductor is always constant. Similarly, using Gauss's law we can get an expression for the electric field at the surface of the conductor. Finally, the most useful property of the conductors is to use them for electrostatic shielding. 

In the external field, the polarisation is always decided by the strength of the electric field. 
To prevent the dielectric breakdown, we need to decrease the potential. For that, we can put positive and negative plates side by side to increase the capacity to store the charge. 
The capacitance is always, like resistance and inductance, is related to the nature of the material and geometrical parameters. The permittivity of a material medium is always equal to dielectric constant times the permittivity of free space. Similarly, we can also explore the series and parallel combination of the capacitor plates. 

The energy stored in the capacitor plates can also be expressed in terms of capacitance, charge, and potential. We will complete this chapter next Monday by discussing the principle, construction, and applications of the Van De Graff generator. 

Please find the board pictures attached herewith.