How Hot Does a Flashlight Bulb Get When Turned On?

[wayneinsane]

This Question is due in 2 Hours... Please Help!

A common flashlight bulb is rated at 0.200 A and 3.80 V (the values of current and voltage under operating conditions). If the resistance of the bulb's tungsten filament at room temperature (20.0°C) is 1.10 , estimate the temperature of the tungsten filament when the bulb is turned on.

 

[LowlyPion]

Please make an attempt to solve the problem and maybe someone will help.

 

[wayneinsane]

Well... what I've tried to do was find the resistance which is R=E/I and I got 3.8/.2 = 19... then I divided that by 1.10 and got 17.27... someone told me to look up in a tungsten chart the value of the new temperature but the chart gives approximations. I've tried 3 attempts, I have 1 left so I can't make anymore approximations... I was wondering if anyone knew a way to find the correct temperature

 

[LowlyPion]

I think you want the increase in resistance with temperature.

Knowing that the ambient resistance is 1.1 and the resistance at power is 19 then you have 17.9 as the increase in resistance with temperature.

See:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/restmp.html

The Temperature Coefficient for Tungsten is .0045
http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/rstiv.html#c1