Question

A charge Q is uniformly distributed over a large plastic plate. The electric field at a point P close to the centre of the plate is 10 V m⁻¹. If the plastic plate is replaced by a copper plate of the same geometrical dimensions and carrying the same charge Q, the electric field at the point P will become
(a) zero
(b) 5 V m⁻¹
(c) 10 V m⁻¹
(d) 20 V m⁻¹

Answer 1

(c) 10 V m^-1

The electric field remains same for the plastic plate and the copper plate, as both are considered to be infinite plane sheets. So, it does not matter whether the plate is conducting or non-conducting.
The electric field due to both the plates,
E = $\frac{\sigma }{{\epsilon }_0}$