1. Ch 5
Conductors, Dielectrics and
Capacitance

21. Let us see what happens a number of electrons are placed on the interior
of a conductor . The electric fields set up by these electrons will repel each other
and accelerate away from each other. Finally these electrons will reach to the
surface of the conductor. The two characteristic of a good conductor are as under.
1 No charge may remain within the conductor. As a final result zero charge
density with in the conductor and a surface charge density resides on the exterior
surface.
2 For the static conditions, no current flows and this leads that the electric
field intensity within the conductor is zero. If it were not zero then it may apply a
Force on the electron in valence band and may constitute a current.

31. 1 Two types of current carriers are present, electrons and holes.
2 Holes are considered as positive charge carriers with μh.
3 Electron with mobility of μe.
4 Both the carrier move in the opposite direction in electric field
but constitute the current in same direction.
5 The conductivity is therefore a function of both hole and electron
concentration and motilities.

34. P modify the E field in the magnitude and direction.
The charge displacement in the form of dipole ,store energy that is
useful in the construction of capacitor.
A conductor with finite conductivity will have a polarization.
A dielectric in an electric field can be viewed as a free-space
arrangement
of microscopic electric dipole composed of +ive and –ive charges whose
center don't coincide.
Dipole charges are not free charges and don’t contribute to the
conduction process.
Dipole are considered as a source of electrostatic field.
All the dielectric materials store electric energy whether they are solid,
liquid or gases and whether or not they are crystalline in nature.
Polar molecules have a permanent displacement between the center of
gravity of +ive and _ive charges.

37. We first consider the tangential
component of electric field
using the relation