(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**

Join Physics Forums Today!

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

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

# Homework Help: Resistance in a wire, sanity check about units.

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