At electrostatic equilibrium, the electric field is zero everywhere inside a conductor, and any charge can only be distributed on the surface of the conductor.
a. true
b. false

True

Explanation:

By applying Gauss  law Electric field is zero everywhere  inside the conductor.

According to Gauss law the net flux of an electric field in a closed surface is directly proportional to the enclosed electric charge.  

For example

For a Gaussian surface inside a conductor all the points have zero electric field as the system is in equilibrium. This implies net flux is zero and net charge inside is zero . So all the charge must be at surface on conductor.          

d

explanation:

v=uf/(u-f)

= 5.10/(5-10) convex lens has positive focal length

=50/-5

=-10 cm (formed at other side)