Physics Help please? This one has got me stumped?

Question

24. (III) A hollow cylindrical resistor with inner radius r1 and outer radius r2, and length l, is made of a material whose resistivity is p (Fig. 25-32). (a) Show that the resistance is given by

R=(p/(2pil)) ln (r2/r1)

for current that flows radially outward. [Hint: Divide the resistor into concentric cylindrical shells and integrate.] (b) Evaluate the resistance R for such a resistor made of carbon whose inner and outer radii are 1.0mm and 1.8mm and whose length is 3.0cm. (c) What is the resistance in part (b) for current flowing parallel to the axis?

Answer 1

You have 2pil in the equation. Is that a typo? I don't see what 'i' is for. R should be a function of p, r1, r2, and l only.

Edit: OK, pi is not p times i, it is pi :-). I agree the result is
R= (p / 2*pi*l) * ln(r2/r1)

But, what part has you stuck? You don't think someone is just going to do your homework for you do you?