Acurrent i flows down a wire of radius a.
(a) if it is uniformly distributed over the surface, what is the surface current den- sity k?
(b) if it is distributed in such a way that the volume current density is inversely proportional to the distance from the axis, what is j(s)?

Part a)

Part b)

here we know that L = length of the wire

Explanation:

Part a)

Current density is given as

since current is uniformly divided across the crossection of the wire so it is given as

Part b)

As we know that volume current density is inversely proportional to the distance from the axis

So we will have

so we have

here we know that L = length of the wire

current and voltage can both be different in different parts of a circuit so it matters where you place the ammeter and voltmete