A positive charge q is placed in front of conducting solid cube at a distance d from its centre. Find the electric field at the centre of the cube due to the charges appearing on its surface.

Explanation

Here `vec(E)_(1)=vec(E)` electric field due to induced charges and `E_(q)=` electric field due to charge q
We know that net electric field in a conducting cavity is equal to zero.
i.e. `vec(E)=vec(0)` at the centre of the cube.
`implies vec(E)_(i)+vec(E)_(q)=vec(0)`
`implies vec(E)_(1)=-vec(E)_(q) implies vec(E)_(1)=- (kq)/d^(2) vec(PO)`