Easy resistance problem

  • Thread starter chris85
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  • #1
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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

 

Answers and Replies

  • #2
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can anybody help?
 
  • #3
learningphysics
Homework Helper
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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
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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
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could it be a problem with my calculator??
 
  • #6
learningphysics
Homework Helper
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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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