Question

What is the resistance of a 1.0m -long copper wire that is 0.30mm in diameter?

What is the resistance of a 17cm -long piece of iron with a 1.5mm

Answer 1

resistance R = (rho*l)/A

rho is resistivity of the material

l is length of the wire

A is area of cross section

A) for copper
resistivity rho = 1.68*10^-8 ohm-m

resistance R = (rho*l)/A

A = pi*(D/2)^2 = 3.142*(0.3/2)^2*10^-6 = 7.06*10^-8

R = (1.68*10^-8*1)/(7.06*10^-8) = 0.237 ohm

B) given l = 17 cm = 0.17m

A = 1.5*1.5 = 2.25*10^-6 m^2

R = rho*l/A
resistivity of iron rho = 9.71*10^-8 ohm-m

R = (9.71*10^-8*0.17) / (2.25*10^-6)

R = 0.0073364 ohm = 7.3364*10^-3 ohm