]1. A 1.3 cm length of tungsten filament in a small lightbulb has a resistance of 0.032 ohms. Find its diameter.(adsbygoogle = window.adsbygoogle || []).push({});

Given: Length= 1.3 cm= .013m

R= 0.032 ohms

resistivity= 5.6e-8 ohms*meter

2.

A= pi (r^2)

R= resistivity (Length/ Area)

3. The attempt at a solution

R= resistivity ( Length/ pi* (r^2) )

.032 ohms= (5.6e-8 ohms*meter) * (.o13m/ (pi* (r^2)) )

.032 (pi) (r^2) = 7.28e-10

.100530965 (r^2) = 7.28e-10

r= 8.509e-5

diameter= 2r= 1.701e-4m

It asks for the answer in mm, so I divided my answer by 1000= 1.7 e-7 mm, but it's not correct = (

What am I missing?

Thanks in advance!

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# Homework Help: Resistivity of tungsten filament

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