Electrostatic Potential and Capacitance 2

Question 1

Inside a conductor, electrostatic field is zero. justify

Answer 1

-In the static situation, when there is no current inside
or on the surface of the conductor, the electric field is zero everywhere
inside the conductor.

-Even when a conductor is placed in an external electric field, the electrons begin to move in the direction opposite to the field.

–ve charges are induced towards the +ve side of the electric field and +ve charges towards the -ve side of the field. This happens until the Net external field= net internal field,

hence net field inside the conductor is 0

Question 2

At the surface of a charged conductor, electrostatic field
must be normal to the surface at every point. justify

Answer 2

If E were not normal to the surface, it would have some non-zero
component along the surface. Free charges on the surface of the conductor
would then experience force and move.

This would produce a current but there is no current in the static situation.

In the static situation, therefore,
E should have no tangential component. Thus electrostatic field at the
surface of a charged conductor must be normal to the surface at every
point

Question 3

The interior of a conductor can have no excess charge in
the static situation. justify

Answer 3

A neutral conductor has equal amounts of positive and negative charges
in every small volume or surface element. When the conductor is charged,
the excess charge can reside only on the surface in the static situation.
This follows from the Gauss’s law. Consider any arbitrary volume element
v inside a conductor. On the closed surface S bounding the volume
element v, electrostatic field is zero. Thus the total electric flux through S
is zero. Hence, by Gauss’s law, there is no net charge enclosed by S. But
the surface S can be made as small as you like, i.e., the volume v can be
made vanishingly small. This means there is no net charge at any point
inside the conductor, and any excess charge must reside at the surface.

Answer 4

Since E = 0 inside the conductor
and has no tangential component on the surface, no work is done in
moving a small test charge within the conductor and on its surface. That
is, there is no potential difference between any two points inside or on
the surface of the conductor. Hence, the result. If the conductor is charged,electric field normal to the surface exists; this means potential will be
different for the surface and a point just outside the surface.

E= -dV/dr

E=0 (insdie conductor)

=> Dv=0

so potential is constant

Question 5

what is electrostatic shielding

Answer 5

Whatever be the charge and field
configuration outside, any cavity in a conductor
remains shielded from outside electric influence: the
field inside the cavity is always zero. This is known
as electrostatic shielding.

The phenomenon of making a system free from electric field is called electrsostatic shielding.
it is based on the fact that the total electric field inside a conductor is 0

Question 6

why is it advised to sit in the car during a thunderstorm

Answer 6

• The metallic body of the car gives rise to electrostatic shielding.