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A lightbulb has the power rated Pn=40W and the temperature of filament, during the...

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fromici | Student | (Level 2) Honors

Posted June 30, 2009 at 12:27 AM via web

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A lightbulb has the power rated Pn=40W and the temperature of filament, during the functioning T=2200c degrees. How much power does the lightbulb

 How much power does the lightbulb consume right off, during signing in, if the thermal coefficient of tungsten is A=4.5*10^-3 K^-1

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giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted June 30, 2009 at 3:23 AM (Answer #1)

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Ro is the resistance of filament at 0C degree, then:

Pn=U^2/[Ro(1+At)]

Po=U^2/[Ro(1+Atc)], where tc=the filament temperature at room temperature (t=20 C degrees)

Po=Pn(1+At)/(1+Atc)=400 W!

We've noticed that the result is 10 times bigger than the rated power Pn=40 W, that's way lightbulbs are damaged when the light is turned on!

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