TP 21.15

Given: l = 6.90 m

d = 0.330 mm

DV = 12.0 V

I = 2.10 A

(a) Find: r - ?

Ohm's Law:

DV = I R

R = DV/I

On the other hand:

R = r l /A

Hence

DV/I = r l /A

r = (DV A) / (I l)

r = (12.0 V)(p(0.330 x 10^-3 m)² /4) / ((2.10 A)(6.90 m)) = 7.08 x 10^-8 W-m