# Current and Ohm's Law-filament diameter

current and Ohm's Law--filament diameter

## Homework Statement

A standard 100 W (120 V ) lightbulb contains a 8.50 cm -long tungsten filament. The high-temperature resistivity of tungsten is 9.0*10^-7.

## Homework Equations

Power=I$$\Delta$$V=$$\Delta$$^2/R
J=I/A

## The Attempt at a Solution

I know power, $$\Delta$$V, and R and am solving for either r or d.
I can use the first equation to solve for I. And then I want to use the second equation because it is the only equation that I've found that uses area (and thus r and d), but I don't know J. Any suggestions? Thanks!