Page 4 - Lesson Note - 1

It happens due to the fact that no electric field exist inside a charged hollow conductor. Potential
inside a shell is constant. In this way we can also conclude that the field inside the shell (hollow
conductor) will be zero.

Dielectric
Dielectrics are of two types Non-polar Dielectric The non-polar dielectrics (like N 2, O 2, benzene,
methane) etc. are made up of non-polar atoms/molecules, in which the centre of positive charge
coincides with the centre of negative charge of the atom/molecule.
Polar Dielectric
The polar dielectric (like H 2O, CO 2, NH 3 etc) are made up of polar atoms/molecules, in which the
centre of positive charge does not coincide with the centre of negative charge of the atom.
Capacitor
A capacitor is a device which is used to store huge charge over it, without changing its
dimensions.

When an earthed conductor is placed near a charged conductor, then it decreases its potential
and therefore more charge can be stored over it.

A capacitor is a pair of two conductors of any shape, close to each other and have equal and
opposite charges.

Capacitance of a conductor C = q / V

Its 81 unit is coulomb/volt or farad.

-6
Its other units are 1 μ F = 10 F
-12
1 μμ F = 1 pF = 10 F
-1 -2 4 2
Its dimensional formula is [M L T A ].
Capacitance of an Isolated Spherical Conductor
C = 4 π ε o K R

For air K = 1

9
∴ C = 4 π ε o R = R / 9 * 10
Parallel Plate Capacitor
The parallel plate capacitor consists of two metal plates parallel to each other and separated by a
distance d.

Capacitance C = KA ε o / d
For air capacitor C o = A ε o / d
When a dielectric slab is inserted between the plates partially, then its capacitance.