Question

Two wires A and B of equal length and circular cross section are made of the same metal, but the resistance of wire B is four times that of wire A. What is the ratio between their spokes ?: a) rB / rA = 2, b) rA / rB = 2, c) rB / rA = 4, d) rA / rB = 16

Answer 1

Answer:

   Option B is the correct answer.

Explanation:

We have resistance $R=\frac{\rho l}{A}$

The resistance of wire B is four times that of wire A

        $R_B=4R_A\\\\\frac{\rho_B l_B}{A_B}=4\times \frac{\rho_A l_A}{A_A}\\\\\frac{A_A}{A_B}=4\\\\\frac{\pi r_A^2}{\pi r_B^2}=4\\\\\frac{r_A}{r_B}=2$

    Option B is the correct answer.