Waves Continued Interference Doppler Effect Bow Waves Wave

Waves Continued… Interference, Doppler Effect, Bow Waves

Wave Interference • Constructive – wave amplitudes add as waves pass through each other • Destructive – wave amplitudes subtract as waves pass through each other

Aspects of Wave Propagation: Interference Constructive Interference Destructive Interference

http: //www. philtulga. com/subtraction. html Beat Frequencies 256 Hz 260 Hz Beat frequency = 4 Hz Tone heard = 258 Hz

http: //www. youtube. com/watch? v=-8 a 61 G 8 Hvi 0&feature=related Interference http: //www. youtube. com/watch? v=5 Pmna. Pv. Av. QY&feature=related Destructive Constructive

Applications of Interference • Can be used to determine distance between sources (size of atoms or molecules in a crystal) • Used to create holograms • Creation/prevention of “dead” spots in music auditoriums • Tuning of instruments (beat frequencies) • Seen in soap bubbles or oil slicks

Your Phone Frequencies (DTMF) Example: When 4 is pushed a 770 Hz and 1209 Hz tone are sent together. The central office detects and deciphers the combined tones. NOTE: the older rotary phones denoted the number dialed by an equivalent number of clicks

Doppler Effect

Aspects of Wave Propagation: Doppler Effect Bug bouncing up and down in the water while otherwise stationary. Observers at points A and B record the same wave frequency. Bug bouncing up and down in the water while moving toward the right. Observer at point B records a higher frequency than observer at point A.

Doppler Effect Frequency produced by horn is constant but if car moving, observers hear different frequency (higher if car moving toward them, lower if car moving away).

Doppler Effect with Light Normal Hydrogen spectrum from a star Red-shifted: lines toward lower frequency - object moving away Blue-shifted: lines toward higher frequency - object moving toward us

Echolation - Doppler Radar Colors represent different echo intensities (reflectivity) - higher reflectivity corresponds to stronger rain rate. Rotation can also be detected by doppler shift.

Aspects of Wave Propagation: Bow and Shock Waves • If the speed of the source is greater than the speed of the waves, the waves “pile up” in the forward direction and cause a V-shape – Example - A boat speeding across a lake creates a wake that is a shock wave Demo: http: //www. phy. ntnu. edu. tw/java/Doppler. html http: //www. phy. ntnu. edu. tw/ntnujava/index. php? topic=873. 0

Bow Waves and Shock Waves hctaw/moc. ebutuoy. www//: ptth M ma tah. W ? raeh oc. ebutuoy. www//: ptth reirra. B dnuo. S gnikaer. B : oedi. V

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