1 / 16

Announcements 10/13/10

Announcements 10/13/10. Prayer Change to reading assignment: For Friday: 18.2 – 18.6 For Monday: 18.7 and PpP 4.1 Exams graded, returned to boxes. See email. Tutorial Lab will be a bit understaffed this Friday and Saturday because many TAs will be at a conference.

stasia
Download Presentation

Announcements 10/13/10

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Announcements 10/13/10 • Prayer • Change to reading assignment: • For Friday: 18.2 – 18.6 • For Monday: 18.7 and PpP 4.1 • Exams graded, returned to boxes. See email. • Tutorial Lab will be a bit understaffed this Friday and Saturday because many TAs will be at a conference. • A student asked me if you could ever have a situation where the group velocity and phase velocity were in different directions. I found out you can very easily create animated gifs with Mathematica, so here is his answer: http://www.physics.byu.edu/faculty/colton/courses/phy123-fall10/weirdwave.gif

  2. Thought question: • You have a 1 volt amplitude sine wave. You want to go up 3 dB in power. How many volts do you need? (Recall: Power ~ amplitude2; true for voltages as well as waves on a string) • 1 V • 2 V • 3 V • 2 V • 3 V

  3. Plane Waves

  4. Spherical Waves

  5. Doppler Effect • What happens if the source is moving? • What happens if the observer is moving? • Key point: Frequency is _______________when the source and observer approach each other, ______________ when they go away from each other • Demo: Doppler Speaker • Stokes Come, Come, Ye Saints recording • http://stokes.byu.edu/bells.wav

  6. The Pie Factory vbelt • Spacing between pies = ? •  = v/f • vs source speed • vo observer speed • v speed of sound (vbelt) • If observermoves toward source (pie maker), she would measure the same ___________ but the pies are coming at her at a faster ________ • If sourcemoves toward observer, the __________ shrinks, but the pie _______ doesn’t change f = vnew/lold f = vold/lnew wavelength speed wavelength speed

  7. Doppler, cont. • Stokes Flash video • http://stokes.byu.edu/doppler_script_flash.html • Combine both effects: • What does  mean?

  8. Thought Question • On a particularly windy day the wind is blowing at half the speed of sound. If I am standing still and a cow is flying towards me at the same velocity as the wind, by what factor will I hear his mooing shifted in frequency? • f’ = (1/2) f • f’ = (2/3) f • f’ = (3/2) f • f’ = 2 f • None of the above.

  9. Thought Question • If I am standing still and a cow is also standing still, by what factor will I hear the frequency his mooing shifted by if the wind is blowing at half the speed of sound in the direction from the cow to me. • f’ = (1/3) f • f’ = (2/3) f • f’ = f • f’ = 3 f • None of the above.

  10. Doppler shift of light • Light source (galaxy) traveling toward you: frequency will _____, wavelength will _____. • See HW 19.4 for equation

  11. Astronomy • How far away is a galaxy? Hard question • Edwin Hubble, 1929: Distance away proportional to speed • Distance measured through supernovae observations • How did he measure speed? • Doppler shift of spectral lines! • That’s now a standard technique for today’s astronomers when they want to measure distances… just measure Doppler shift. • Hubble’s Law and the Big Bang • (Yes, it’s OK for LDS to believe in the Big Bang…)

  12. Sonic Boom • http://stokes.byu.edu/boom_flash.html • http://stokes.byu.edu/boomray_script_flash.html • Happens with all types of waves whenever the sources is traveling faster than the speed of the wave… …so, what is “sonic boom” of water waves?

  13. θ Sonic Boom Sonic boom manifested by condensation of water in air sinq = vsound/vsource = 1/“Mach number”

  14. Sonic Boom Sonic boom of bullet in flight (holographic interferometry?) • How fast is the bullet traveling? • Mach # = 1/sinq

  15. Reading Quiz • Which term did not appear in the discussion of wave interference for today’s reading assignment? • antinode • constructive • destructive • path length • superposition

  16. Ripple Tank image: wikipedia Interference • Path length • Constructive • Destructive • Video: Two outdoor speakers • Demo: Moire pattern transparencies • Demo: Hearing test • Demo: 2-speaker interference • Speed of sound = ?

More Related