Class 12 NEET Physics Electrostatics Questions Part 1

There are eight corners of a cube and in each corner there is a charge of (−q). At the centre of the corner there is a charge of (+q) Each corner is equidistant from the centres of the cube and the distance (d) is half of the diagonals of the cube.
Diagonal of the cube =√b2+b2+b2 =√3b
∴d=

√3b

2

Now, electric potential energy of the charge (+q) due to a charge (−q) at one corner =U
=

q1q2

4πε0r

=

(+q)×(−q)

4πε0(√3b∕2)

=−

q2

2πε0(√3b)

∴ Total electric potential energy due to all the eight identical charges =8U=

−4q2

√3πε0b