You are Here: Home >< Physics

# Resistivity Question watch

1. Hi.

Can someone please see if I am approaching this question in the right way ?

Q: Consider the filament of a 230 V 100 W lamp made from 500 mm Tungsten at resistivity (7 x 10^-7). What is the radius of the filament wire ?

Using P=IV, 100=230i so current is 0.43 A. Now find resistance by R= V/I so (230/0.43) = 535 Ohms. Then substitute into the equation R=pL/A.

Is this the right way to do this question ? Is my resistance correct ?

Thanks
2. Looks it to me. Shove the resistance, resistivity and length into the equation and there you are.
But remember, you need to find radius, not area, so it's area=Pi*r^2
So r=root of (area/pi.)
Or at least, that's what I'd do

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: November 8, 2008
The home of Results and Clearing

### 3,707

people online now

### 1,567,000

students helped last year
Today on TSR

Hang on, have Edexcel's come out already?

### University open days

1. SAE Institute
Animation, Audio, Film, Games, Music, Business, Web Further education
Thu, 16 Aug '18
2. Bournemouth University
Fri, 17 Aug '18
3. University of Bolton