Announcements 10/15/10 Prayer Long list of HW changes/corrections/clarifications, see email Dispersion lab due tomorrow. Labs 4 & 5 starting tomorrow Term project proposal due a week from tomorrow, emailed

to me directly, text in body of email & figures (if needed) as attachments.

a. Syllabus: “The term project is an opportunity for you to propose and conduct a simple experiment or to theoretically, mathematically, or computationally investigate an aspect of the course in more depth.”

b. Groups of 2 are OK. Groups of 3 only with permission.c. At least 15 hours of work (per person, if in a group). d. Guidelines/Grading info:

http://www.physics.byu.edu/faculty/colton/courses/phy123-fall10/project/guidelines.htm

e. Ideas: http://www.physics.byu.edu/faculty/colton/courses/phy123-fall10/project/ideas.htm

f. Some actual projects: http://www.physics.byu.edu/faculty/colton/courses/phy123-fall10/project/actualprojects.htm

Reading Quiz In a standing wave, the points that have

the maximum vibration are called:a. nodesb. antinodes

Standing Waves

Demo: Rubber tubing Web demo, revisited

http://www.colorado.edu/physics/phet/simulations/stringwave/stringWave.swf

Image from Wikipedia

Standing Waves Will occur whenever you have two waves (same

frequency) moving in opposite directionsa. http://www.physics.byu.edu/faculty/colton/courses/phy123-fall10/twotravelingwaves.gif

Math: A cos(kx - t) + A cos(kx + t) From trig.: cos(a–b) + cos(a+b) = 2cos(a)cos(b)

Can occur with a single wave, if it reflects, provided…

1. vibration frequency is right, i.e.2. reflection happens just right

Demos Video: http://stokes.byu.edu/standing_script_flash.html Demo: “Ladies belt”

Videos: Bowling ball, goblet, [Tacoma Narrows bridge] Demo: Trumpet

“Resonance”

Standing Wave Patterns Back to Ladies belt demo

a. What kinds of patterns do you get?b. “node” vs “antinode”

Harmonics

Standing waves on a string: “Closed-Closed”

For stable patterns: L = _______ What are the frequencies? Relative to the fundamental frequency?

L

L=_____

L =_____

L =_____

Standing waves in air: “Open-Open”

Quick writing: draw what you think the second harmonic should look like

For stable patterns: L = _______ What are the frequencies? Relative to the fundamental frequency? Demo: Trumpet, again

Open end Open end

L=_____

Example: organ pipe

Standing waves in air: “Open-Closed”

Quick writing: draw what you think the second, third, and fourth harmonics should look like

For stable patterns: L = _______ What are the frequencies? Relative to the fundamental frequency? Why wasn’t trumpet in this category?

Open end Closed end

L=_____

Standing Waves in 2D

Again, from Wikipedia

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Standing Waves in 3D From Colton and Wienkes, Rev. Sci. Instr., 2009

a. Light waves, frequency = 10 GHz (microwaves)

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Do they exist? Class poll

Demos

PVC pipe vs. Spectrum Lab (skipped for now) Flame standing waves