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?
3 answers
look up the resisitive of tungsten at 1500C. you know area, compute length from known resistance (Power=V^2/R)
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
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
L=RA/p
=(360)*(PI (.0175*10^-3)^2) / (5*10^-7)
L = 0.58m
=(360)*(PI (.0175*10^-3)^2) / (5*10^-7)
L = 0.58m
4 answers