Hello everyone i'm stuck on this problem it says:(adsbygoogle = window.adsbygoogle || []).push({});

A common flashlight bulb is rated at 0.30 A and 2.9 V (the values of the current and voltage under operating conditions). If the resistance of the bulb filament at room temperature (20°C) is 1.4 , what is the temperature of the filament when the bulb is on? The filament is made of tungsten.

I found the Resisivity, p of tungsten to be: 5.25E-8;

Temperature Coeffeicent of Resisivity, [tex]\delta[/tex] to be: 4.5E-3;

Here is the forumla to find Temperature...

[tex]P-Po = Po\delta(T-To)[/tex];

The book doesn't explain the formula at all, all i got out of it was it doesn't matter if you use Kelvin or Celcius for the Temps....

I know To is the Initial temp 20 C, I also found P = V/A = 2.9/.30 = 9.67;

So I think i have everything I need, but the answer is wrong...

[tex]P-Po = Po\delta(T-To)[/tex];

5.25E-8 - 9.67 = 9.67*4.5E-3(T-20);

183.7 = .0435T

T = 4272 C huge number, its wrong

I also tried switching the P's and Po's and got an even bigger number which was wrong, do u konw what i'm doing wrong? Thanks.

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# Homework Help: Finding the temperature of a filament! I have all the values, now where to put them.

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