# Physics

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A 40 W (120V) light bulb has a tungsten filament of thickness 0.035 mm. The filament's operating temperature is 1500 degrees C.

PART A
How long is the filament?

PART B
What is the resistance of the filament at 20 degrees C?

• Physics -

look up the resisitive of tungsten at 1500C. you know area, compute length from known resistance (Power=V^2/R)

• Physics -

Power= V^2/R
40=120^2/R
R=360

R=pL/A
RA/p=L
(360)(pir^2)/(5.0x10^-7)=L
L= 2.77
(5.0x10^7) is the reisisttivity of tugsten at 1500 degrees

• Physics -

sf

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