## 21. If the electrostatic potential were Igiven by $$\phi = {\phi _0}$$ (x^{2} + y^{2} + z^{2}), where $${\phi _0}$$ is constant, then the charge density giving rise to the above potential would be

^{2}+ y

^{2}+ z

^{2}), where $${\phi _0}$$ is constant, then the charge density giving rise to the above potential would be

## 22. Consider an infinitely long straight cylindrical conductor of radius R with its axis along the Z-direction, which carries a current of 1A uniformly distributed over its cross-section. Which of the following statements is correct?

(where, r is the radial distance from the axis of the cylinder)

(where, r is the radial distance from the axis of the cylinder)