]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!

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

Dismiss Notice

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: Resistivity of tungsten filament

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