# Temperature of Bulb Filament

## Homework Statement

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 4.5e10-3

R = V/I

## 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.

Delphi51
Homework Helper
What are the units on that coefficient of resistivity? Perhaps we can make up a formula relating it to temperature and resistance.

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?

LowlyPion
Homework Helper
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?

Delphi51
Homework Helper
Traditionally E instead of V has been used to represent electromotive force
I remember that, Skeptic! I've been in high school for 30 years and all our books and government exams just used V for electric potential, which is a bit confusing leading inevitably to saying "Voltage" instead of "potential". But P and E are busy already so V is a relief.