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# 7 to post (8) - Chapter7 MODEL macroscopicobjects level 7....

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THE QUANTUM MECHANICAL  MODEL Chapter 7

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Two Branches of Mechanical Physics Classical Mechanics  – laws describing the motion of  macroscopic objects Quantum Mechanics  – principles of electrical and  magnetic properties at the atomic and subatomic  level
§7.2  Electromagnetic Radiation All electromagnetic radiation travels in waves.  Waves  have three basic characteristics: 1) Wavelength  ( ) - the distance between the  λ crests or troughs of a wave. 2)  Frequency  (nu,  ѵ ) - the number of waves per  second passing a certain point.  3)  Speed  (c)  – all electromagnetic radiation has  the same speed, the speed of light ( c ): c  = 2.9979  ×  108 m/s

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§7.2  Electromagnetic Radiation All electromagnetic radiation  travels at the speed of light. As wavelength decreases,  frequency increases, and vice  versa: λ↑ ѵ       λ↓ ѵ This reciprocal relationship is:  ∙  λ ѵ   =   c Units of  λ  are in m;  ѵ  are s-1  (hertz).
§7.2  The Electromagnetic Spectrum Electromagnetic radiation is classified based on  λ

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§7.2  Interference Waves interact with each other via interference.  Constructive interference  – two waves add to make a  larger wave Destructive interference  – two waves cancel each other out
§7.2  Diffraction Diffraction   - waves (not particles) bend around an opening  in a barrier. Diffraction through two slits gives an interference pattern of  the diffracted waves.

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§7.2  The Photoelectric Effect Photoelectric Effect -  when exposed to certain light,  metals eject electrons from their surface. It was first predicted that the electron’s energy  would  be proportional to the  intensity  of the light source. According to this theory, if a dim light was used there  would be a lag time before electrons were emitted (to  give the electrons time to absorb enough energy).   a metal
The PE requires a minimum or threshold frequency  of light to occur.  Electrons dislodge  immediately  from metals exposed  to dim light at or above the threshold frequency.   The PE depends on light frequency  not intensity. Higher frequency  higher energy electrons  Higher intensity  more photons  more dislodged electrons §7.2  The Photoelectric Effect

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§7.2  Einstein and the PE Effect Einstein proposed light is a stream of  particles   ( photons,  units or quanta of EMR).
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