A 40 W (120 V) lightbulb has a tungsten filament if thickness 0.030mm. The filam

Question

A 40 W (120 V) lightbulb has a tungsten filament if thickness 0.030mm. The filament's operating temperature is 1500 Celcius degrees. A. How long is the filament? B. What is the resistance of the filament at 20 degrees Celcius? A 40 W (120 V) lightbulb has a tungsten filament if thickness 0.030mm. The filament's operating temperature is 1500 Celcius degrees. A. How long is the filament? B. What is the resistance of the filament at 20 degrees Celcius? A. How long is the filament? B. What is the resistance of the filament at 20 degrees Celcius?

Explanation / Answer

Here ,

resistivity of tungestun , p = 5.6 *10^-8 Ohm.m

a) let the length is L

120^2/40 = 5.6 *10^-8 * L/(pi * (0.030/2 *10^-3)^2) * (1 + (1500 - 20) * .0045)

solving for L

L = 0.593 m

the length of the wire is 0.593 m

b)

let the resistance is R

R = 5.6 *10^-8 * 0.593/(pi * (0.030/2 *10^-3)^2)

R = 47 Ohm

the resistance is 47 Ohm

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