Question

In the electric current flow, it is found that the resistance (measured in the units called ohms) offered by a fixed length of wire of a given material varies inversely as the square of the diameter of the wire. If a wire 0.01 in. in diameter has a resistance of 0.306 ohm, what is the resistance of a wire of the same length and material with diameter 0.0299 in. to the nearest ten-thousandth?

Answer 1

R = k / d^2 (k is a constant, unknown)
d1 = 0.01 and R1 = 0.306
d2 = 0.0299 R2 = ?

Use the equation in line 1 for both case and divide and k will go away and you can find R2

Answer 2

R = k/d^2 ----- (1)
0.306 = k / (0.01)^2 ----- (2)
R = k / (0.0299)^2 ----- (3)
Divide (3) / (2) and solve for R