Question

The instructions for an electric lawn mower suggest that an A gauge extension cord ( cross sectional area = 4.2 x 10-7 m2 ) should only be used for distances up to 35 m. The resistivity of copper (used in the extension cord) is 1.72 x 10-8 .m at 20oC and the temperature coefficient of resistivity of copper is 0.004041 (oC)-1. What is the resistance of a A type extension cord of length 35 m at 40oC

Answer 1

1.43 Ω

Step-by-step explanation:

Given that

Cross sectional area of the cord, A = 4.2*10^-7 m²

Distance meant to be used, L = 35 m

Resistivity of copper, p = 1.72*10^-8 Ωm

Temperature of copper, t = 20° C

Temperature coefficient of copper, t' = 0.004041 °C^-1

To solve this, we would use the resistance and resistivity formula

R = pL / A, on substituting

R = (1.72*10^-8 * 35) / 4.2*10^-7

R = 6.02*10^-7 / 4.2*10^-7

R = 1.43 ohm

Therefore, the resistance of the extension cord is 1.43 ohm