Calculating Resistance of a Light Bulb Filament

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To calculate the resistance of a light bulb filament, the filament's length is 0.72 meters and its radius is 6.0 x 10^-2 mm, which converts to 6.0 x 10^-5 meters. The resistivity of the filament material is 1.2 x 10^-5 ohm meters. Using the formula R = ρL/A, the area is calculated as π times the radius squared, resulting in approximately 1.13097 x 10^-8 m². The calculated resistance is around 763.94 ohms, which rounds to 760 ohms, aligning with the expected answer. Issues with calculator settings and rounding were discussed as potential sources of error.
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Homework Statement

the 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



Homework 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?



The Attempt at a Solution

 
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can anybody help?
 
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
 
hmmm thanks when i enter the pi x (6.0x10^-5)^2 i keep getting 1.1 x 10^-8 i don't get why
 
could it be a problem with my calculator??
 
chris85 said:
could it be a problem with my calculator??

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

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