Wires help???

Question

Wire 1 and wire 2 are made from the same metal. Wire 2 has a larger diameter than wire 1. The electric field strengths E1 and E2 are equal.

A) Compare the values of the two current densities. Is J1 greater than, less, or equal to J2?

B) Compare the values of the currents I1 and I2. Is I1 greater then, less or equal to I2?

Answer 1

Here are some hints.

If the two wires are of the same metal, then the only thing that determines resistance is the diameter -- a larger diameter means there is a larger "pipe" for current to travel down - thus the resistance is lower.  

Resistance goes as 1/area.  

So, if you use Ohm's law, V=IR, but now replace R=k/A (k some constant, same for both wires), you get V=k*I/A

Now the other thing you need to know, is that current density J = is I/A.  Thus V = k*J is used for solving part A.  

And V= k*I/A is used for solving part B.