Question

(a) A steady current flow in a metallic conductor of non- uniform cross-section. Which of these quantities is constant along the conductor: current, current density, electric field drift speed? 

(b) Is ohm’s law universally applicable for all conducting elements? If not, given examples of elements which do not obey ohm’s law. (c) A low voltage supply from which one needs high currents must have very low internal resistance. Why? (d) A high tension (HT) supply, of say 6kV, must have a very large internal resistance. Why? 

Answer 1

(a) Only current is constant. Rest depends on area of cross-section inversely. (b) Ohm’s law is non-universal for example non-ohmic conductors like semi-conductors. 

So low resistance is necessary. 

Because (d) the circuit is shorted accidentally, the current drawn will exceed safely limits.