
#1
Feb109, 12:05 PM

P: 72

1. The problem statement, all variables and given/known data
A common flashlight bulb is rated at 0.3 A and 3.3 V (the values of current and voltage under operating conditions). If the resistance of the bulb's tungsten filament at room temperature (20.0 degrees Celsius) is 1.10 Ohms , estimate the temperature of the tungsten filament when the bulb is turned on. Take the temperature coefficient of resitivity for tungsten to be 4.5e103 2. Relevant equations R = V/I 3. The attempt at a solution R = 3.3V / 0.3A = 11 Ohms when turned on Little lost on how to find the temperature when turned on. 



#2
Feb109, 12:33 PM

HW Helper
P: 3,394

What are the units on that coefficient of resistivity? Perhaps we can make up a formula relating it to temperature and resistance.




#3
Feb109, 01:00 PM

P: 1,784

I'm curious about a custom I see universally in this forum. It's been quite a few years since I was in school and I wonder if this custom indicates a change in the way EE is being taught nowadays. Traditionally E instead of V has been used to represent electromotive force just as I represents current instead of A. In the past a distinction has been made between the unit of electromotive force and its designator.
Are instructors and textbooks now using V for electromotive force? 



#4
Feb109, 01:11 PM

HW Helper
P: 5,346

Temperature of Bulb Filament
How much does the resistance of the filament change?
With that Δ in resistance perhaps you can figure the Δ in temp needed to develop that much resistance? 



#5
Feb109, 01:35 PM

HW Helper
P: 3,394





#6
Feb109, 01:40 PM

P: 13

Problem is ez.
You have found the R. That's good! Look at this website to know more about the coefficent. You will figure out. http://hyperphysics.phyastr.gsu.edu...ic/restmp.html 


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