phys3313-lec7 - Physics 3313 - Lecture 7 Wednesday...

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Physics 3313 - Lecture 7 9/16/2009 1 3313 Andrew Brandt Wednesday September 16, 2009 Dr. Andrew Brandt 1. HW2 due and HW3 assigned 2. Phase Velocity 3. Wave Equation 4. Group Velocity
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Phase Velocity How fast do dB waves travel? Might guess wave has same velocity as particle One speed associated with a wave is the phase velocity We have an expression , but what’s nu? so Thus ! Oops, with v < c this means that , so phase velocity cannot be correct speed of particle represented by de Broglie waves. 9/16/2009 3313 Andrew Brandt 2 22 E hv mc hv mc γγ == ⇒= 2 mc h γ ν= v vv p mc h c hm = v p νλ = /v λγ = v p c >
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Wave Equation 9/16/2009 3313 Andrew Brandt 3 cos2 y A vt π = ( ) v p x y A vt = Want to develop an expression for displacement y as a function of position and time Consider a string If I oscillate the string, each point on the string will move up and down with time So if I define the maximum displacement in y as amplitude A at x=0 at a time t=0, then I can describe the displacement as a function of time at x=0 using: At t=0 x=A, at t=T/4 x=0, at t=T/2 x=-A etc.
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This note was uploaded on 10/21/2009 for the course PHYS PHYS 3313 taught by Professor Andrewbrandt during the Fall '09 term at UT Arlington.

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phys3313-lec7 - Physics 3313 - Lecture 7 Wednesday...

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