# Easy resistance problem

1. Oct 11, 2007

### chris85

1. The problem statement, all variables and given/known datathe filament of a 230V light bulb is 0.72M long and has a radius of 6.0 x 10^-2mm. The resistivity of the filamen metal is 1.2 x 10^-5 ohm metres. Work out the resistance of the bulb

2. Relevant equations I have tried working out the area using pi x radius square but am having trouble converting 6.0x10^-2mm into metre square.

i am using R=pL/A so i did 1.2x10^-5 x 0.72/1.1 x 10^-8m^2 which equals 785 ohms but the answer is 760 ohms can anyone please help me out?

3. The attempt at a solution

2. Oct 11, 2007

### chris85

can anybody help?

3. Oct 11, 2007

### learningphysics

I think the problem is with your rounding...

I get 763.94ohms... which when taken as 2 sig figs is 760ohms.

convert 6.0*10^-2mm to m first

6.0*10^-2mm * 1m/(1000mm) = 6.0*10^-5m

area is pi*(6.0*10^-5m)^2 = 1.13097*10^-8 m^2

4. Oct 11, 2007

### chris85

hmmm thanks when i enter the pi x (6.0x10^-5)^2 i keep getting 1.1 x 10^-8 i dont get why

5. Oct 11, 2007

### chris85

could it be a problem with my calculator??

6. Oct 11, 2007

### learningphysics

set your calculator to scientific notation. then you should see the other digits.