Question

The heating element of a simple heater consists of a 2.2m--long, 0.70mm--diameter nichrome wire. When plugged into a 120 V outlet, the heater draws 7.5 A of current when hot.

I found that the wire's resistance when it was hot was 16 ohms. Now using this answer of 16 ohms calculate the resistivity of nichrome in this situation in units of ohms * m.

I can not get the answer. I have been using the formula R=pL/A which I rearranged to p=RA/L.

I got A by A=pie(7*10^-4)^2, which equals 1.54*10^-6.

I plugged in the numbers p=(16)(1.54*10^-6)/(2.2m) and got the answer 1.12*10^-5 but this isn't the right answer. I can not figure out what I did wrong. I would appreciate any help that gets me to the right answer! Thank you!!

Answer 1

You need to divide the diameter by two because the equation requires the radius not the diameter.