Question

An inverse square law of distance is obeyed by :

• A. the force per unit length between two long straight parallel current-carrying conductors in vacuum.
• B. the electric field intensity outside an isolated charged sphere.
• C. the magnetic flux density outside a long straight current-carrying wire.
• D. the electrostatic potential.

Answer 1

The correct option is B the electric field intensity outside an isolated charged sphere.

For a isolated charged sphere, of radius R, the electric field is seen to be identical to that of a point charge Q at the center of the sphere. Since all the charge will reside on the conducting surface, so field intensity at a distance $r>R$ will be :
$E=\frac{Q}{4\pi {ϵ}_0{r}^2}$ . So E obeys inverse square law of distance.