Find Diameter of Tungsten Filament of Resistance 0.041

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To find the diameter of a tungsten filament with a resistance of 0.041 ohms and a length of 2.5 cm, the resistivity of tungsten (5.6 × 10−8 Ω·m) is used in the formula R = ρ(L/πr²). The user attempted to rearrange the equation but arrived at an incorrect value for the radius. Other participants suggested checking for errors in decimal placement during calculations. The discussion emphasizes the importance of careful mathematical manipulation to ensure accurate results.
bob12345
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Homework Statement



A 2.5 cm length of tungsten filament in a
small lightbulb has a resistance of 0.041
.
Find its diameter. (The resistivity is
5.6 × 10−8
· m).
Answer in units of mm.

Homework Equations


R=p(L/pi*r^2)


The Attempt at a Solution


i have reworked the equation to the square root of pL/R*pi equals r and then multiplied that answer by 2 which nds u being 2.0856e-4 but it is not right??
 
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Welcome to PF!

Hi bob12345! Welcome to PF! :smile:

(have a pi: π and a rho: ρ and try using the X2 tag just above the Reply box :wink:)

Method seems ok :smile: …

have you just got the decimal point in the wrong place before square-rooting?
 
i didnt think so because i converted the length to meters..
 

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