How Hot Does a Flashlight Bulb's Filament Get When Turned On?

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Homework Help Overview

The discussion revolves around estimating the temperature of a tungsten filament in a flashlight bulb when it is turned on, given its rated current and voltage, as well as its resistance at room temperature. The problem involves concepts from electrical engineering and thermodynamics.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the calculation of resistance based on voltage and current, and question how to relate resistance changes to temperature changes. There is also inquiry into the units of the temperature coefficient of resistivity and its application in the context of the problem.

Discussion Status

The discussion is active with various participants exploring different aspects of the problem. Some have provided insights into the relationship between resistance and temperature, while others are questioning the conventions used in electrical terminology. No consensus has been reached on the approach to solving the problem.

Contextual Notes

Participants note potential confusion regarding the terminology used for electromotive force and its representation in current educational materials, reflecting on changes in teaching practices over time.

JJones_86
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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

Homework Equations



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.
 
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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?
 
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?
 
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.
 

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