Please answer me these questions with explanation related to electrostatic

Dear student,

The electric field inside the conductors is zero. So charges will be induced on the inner surface of the sphere such that the electric field inside the conductor is zero. Hence the inner surface of the sphere induces chargeand the outer thus aquires.

Work done per unit charge in bringing a charge from infinity to its surface is.
Further, there is no electric field inside. Hence no work is done in bringing the charge from surface to point A.
Hence the potential at point A is

Dear student,

In question 28, the electric field between the two plates due to charge densitiesis
.
But this field is in horizontal direction only, and the displacement is in both horizontal and vertical directions. Hence the work due to electric force on charge due to displacement only in horizontal direction.
Hence