Phys 141 Sound and Acoustics HOMEWORK ASSIGNMENT #2 (Due 4:30 pm, Monday. Februa

Question

Phys 141 Sound and Acoustics HOMEWORK ASSIGNMENT #2 (Due 4:30 pm, Monday. February 19, 2018) 1) 2 pts Two waves of the same frequency have amplitudes Im and 2m. In traversing the same medium, they undergo interference. a) If the interference is totally constructive, then the amplitude is m. b) If the interference is totally destructive, then the amplitude ism 2) 1 pt Two sine waves with frequencies 300Hz and 302Hz are played simultaneously. Calculate the frequency ofthe "beats". 3) 2 pts You are tuning a piano using a middle A tuning fork with a frequency of f-440 Hz. You hit the middle·A' key of the piano and the tuning fork, and hear beats at a frequency or Hz. That piano key has a frequency of either Hz. 4) 3 pts The effect is the apparent shift in frequency observed when the source or the observer is in relative motion. When they are moving towards each other, the frequency appears ( (choose higher/lower); when they are moving away from each other, the frequency appears ( (choose higher/lower). 5) 1 pt The perceived pitch is correlated to the physical property of 6) 1 pt The perceived loudness is correlated to the physical property of 7) 1 pt The perceived tone quality (timbre) is correlated to the physical property of 8) Two identical loudspeakers, emitting pure tones with the same frequency (f- 343 Hz) but not necessarily in phase and with different amplitudes IA and 3A, are placed next to each other. The temperature is 20, so the speed of sound is 340 ms. a) 3 pts If the relative phase is such that the interference is totally constructive, what are the amplitude of the resulting combined wave? b) 3 pts If the relative phase is such that the interference is totally destructive, what are the amplitude of the resulting combined wave? c) 3 pts Now, the amplitudes of the waves are adjusted to be equal with cach loudspeaker emitting at 2A, but the frequency of the wave from one speaker is adjusted up to 344 Hz (the other remained 343Hz). (0)What is the name of the phenomenon that will happen when two speakers played together? (ii)What is the period of this phenomenon?

Explanation / Answer

1a) for constructive interference, amplitude = 1 + 2 = 3m

1 b) for distructive, amplitude = 2-1 = 1 m

2] beat frequency = f1-f2 = 302-300 = 2 Hz

3] f = f1 +- fb = 440 +-2 = 438 Hz or 442 Hz

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