7.3 Lightbulbs

7.3 Lightbulbs - Observations about Lightbulbs Key...

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1 Key Concepts: 1. Light 2. Blackbody Spectrum 3. Color/Temperature 4. Thermal Expansion in Solids Observations about Lightbulbs • Lightbulbs glow yellow-white • They get very hot during operation • You can feel heat radiating from them • They eventually burn out • They come in many wattages • They come in many specialized types Question 1 How does a lightbulb produce light? Incandescent Bulb • Tungsten filament produces light • Electrical connections deliver power to filament • Glass envelope protects filament • Nitrogen/Argon/Krypton gas fill prolongs life Question 2 What determines a lightbulb’s color? Thermal Radiation • All materials emit thermal radiation – All materials contain electric charges – Thermal energy causes those charges accelerate Accelerating charges emit electromagnetic waves Hotter temperatures yield shorter wavelengths
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2 Color Light is characterized by frequency, or more commonly, by wavelength 1 m = 10 9 nm 1 m = 1,000,000,000 nm 1 nm = 10 –9 m 1 nm = 0.0000000001 m Visible Light (approx): 700 nm 550 nm 400 nm A nanometer is very small Black Body Spectrum The spectrum and intensity of electromagnetic waves from a black body depend only on its temperature BB Radiation Applications • Remote sensing • Temperature of stars Which star is hottest? Clicker Question 1 A B C D E F G Filament Temperature and Color • Filament behaves as a (nearly) black body – It emits a spectrum characteristic of its temperature
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This note was uploaded on 02/07/2010 for the course PHY 1405 taught by Professor Russell during the Fall '07 term at Baylor.

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7.3 Lightbulbs - Observations about Lightbulbs Key...

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