Calculating Resistance of a Light Bulb Filament

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Homework Help Overview

The discussion revolves around calculating the resistance of a light bulb filament, given its dimensions and material properties. The problem involves the application of the resistance formula R = ρL/A, where the resistivity, length, and cross-sectional area of the filament are provided.

Discussion Character

  • Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the conversion of the filament's radius from millimeters to meters and its impact on area calculation. There are attempts to verify the resistance calculation and concerns about rounding and significant figures.

Discussion Status

Some participants have offered guidance on converting units and calculating the area, while others are exploring potential issues with rounding and calculator settings. Multiple interpretations of the calculations are being examined, but no consensus has been reached regarding the final resistance value.

Contextual Notes

Participants are navigating through unit conversions and significant figures, which may affect their calculations. There is also mention of potential calculator settings that could influence the results.

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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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