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I. Blackbody Radiation and Planck’s Hypothesis a. Thermal radiation – an object at any temperature emits electromagnetic radiation i. Spectrum of radiation depends on the temperature and properties of the object. ii. Consists of a continuous distribution of wavelengths from the infrared, visible, and ultraviolet b. Classical viewpoint – thermal radiation originates from accelerated charged particles near the surface of an object. Charges have a distribution of frequencies, which account for the spectrum. c. Blackbody – an ideal system that absorbs all radiation incident on it. (Ex: a small hole leading to the inside of an hollow object) i. Radiated energy varies with wavelength and temperature. As the temperature of the blackbody increases, the energy it emits increases. Also, the peak of the distribution shifts to shorter wavelengths. Obeys Wien’s displacement law . ii. Sun appears white, hotter stars appear blue, and cooler stars appear orange or red. d. Classical theories agree for long wavelengths, but not short wavelengths. Planck developed a formula for blackbody radiation. i. Blackbody radiation was produced by submicroscopic charged oscillators called resonators . ii. where 1. n – is a positive integer called a quantum number 2. Energy can only have discrete values. Energy is quantized. Each discrete energy value represents a different quantum state. II. The Photoelectric Effect and the Particle Theory of Light a. Photoelectric effect – light incident on certain metallic surfaces caused the emission of electrons from the surfaces. Emitted electrons were called photoelectrons . i. Stopping potential – when V is equal to or more negative than - V s , no electrons reach C and the current is zero. Independent of the radiation intensity. 1.
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This note was uploaded on 10/20/2008 for the course PHYS 2070 taught by Professor Thompson during the Spring '08 term at Toledo.

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