(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A x cm long wire has a diameter of y mm and a resistivity of 4.0x10-7 ohm-cm. Calculate its resistance.

2. Relevant equations

R = p*L/A

3. The attempt at a solution

First, I convert the given information into SI units:

Length = x*10^-2 m

Diameter = y*10^-3 m

Resistivity = 4*10^-5 ohm/m

Next, cross-sectional area of a wire/cylinder is pi*r^2 = pi*(d/2)^2 = (1/4)pi*d^2

R = p*L/A = p*L/((1/4)pi*d^2) = (4 L p)/(d^2 pi)

If x = 20 cm and y = 0.3mm,

R = (4*20*10^-2 *4*10^-5)/((0.3*10^-3)^2*Pi) = 113.177 ohms

Is this correct? My TA told me that I converted the units wrongly, and that the correct answer is 0.0113177 ohms.

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Resistance in a wire, sanity check about units.

**Physics Forums | Science Articles, Homework Help, Discussion**