Homework help- electrical resistance

AI Thread Summary
To find the diameter of a tungsten filament with a resistance of 0.041 ohms, a length of 2.5 cm, and a resistivity of 5.6 × 10−8 ohm-meter, the formula R = ρ(L/(πr²)) is used. The user reports consistently getting an incorrect answer of 20856 m, indicating a potential error in unit conversion or calculation. It is essential to ensure that all measurements are in the correct units, particularly converting the length to meters and calculating the radius accurately. The discussion emphasizes the importance of careful unit management in physics problems. Clarifying the calculation steps may help identify the source of the error.
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/2pi*rsquared)

The Attempt at a Solution


i keep getting 20856 m as my answer but it is wrng when i entr it i plugged in everything and made sure everything was to the right unit so don't know what is wrong
 
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Take care of units. The resistance of the filament is 0.041 ohm, the resistvity is 5.6 x10-8 ohm-meter, and the length is 0.025 m. How could you get such a result for the diameter of a tiny filament? Show your calculation.

ehild
 

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Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
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