Interference and Doppler Questions Interference in Space Interference

Interference and Doppler • • Questions? Interference in Space Interference in Time (Beats) Doppler Shift – Source moving – Observer moving – Both moving – Examples

Interference in Space • Occurs when 2 waves - of same frequency and wavelength combine constructively or destructively because of different propagation paths. – Two loudspeakers (stereo) animation – Example 12 -12 – FM car radio – AM car radio – (cellphone) – Noise-cancelling headphones – Diffraction gratings

Interference in Space Animation • Two loudspeakers • Two speaker animation Note: this is Java, not Flash http: //phet. colorado. edu/en/simulation/sound

Example 12 -13 •

Interference in Time • Occurs when 2 waves - of slightly different frequency and wavelength - combine constructively or destructively with the variation in time. • Produce “Beat” frequencies – Instrument tuning – Superheterodyne radio receiver – Doppler weather radar

Interference in Time Derivation •

Interference in Time Animation • Beats in time • Animation http: //faraday. physics. utoronto. ca/PVB/Harrison/Flash/Class. Mechanics/Beats. html (go to the last scene)

Example 12 -3 •

Superheterodyne radio receiver • For FM, local oscillator always 10. 7 MHz above desired station frequency • Beat frequency of 10. 7 MHz emerges. • Can build very selective 10. 7 MHz filters!

Doppler Shift (Source moving toward) •

Doppler shift • Frequency and/or wavelength changed due to motion of source and/or listener • Animation (moving source) http: //faraday. physics. utoronto. ca/PVB/Harrison/Flash/Class. Mechanics/Doppler. Effect. html (Play scene 1) http: //www. upscale. utoronto. ca/PVB/Harrison/Flash/Class. Mechanics/Doppler. Wave. Front s. html (Break the sound barrier!)

Doppler Shift (Observer moving toward) •

Example 12 -14 •

Example 12 -15 •

Problem 54 - Bat squeaking •

Doppler Shift for Electromagnetic Waves • Doppler weather radar • Red shift (Bell Labs – Cosmic background radiation) https: //en. wikipedia. org/wiki/Discovery_of_cosmic_microwave_background_radiation

Problem 55 - Tubas and Beats •

Problem 56 – Blood flow •

Medical Applications • High pressure Low pressure flow

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