Determine the speed of the wave. A) 0.01 m/s B) 0.02 m/s C) 0.03 m/s D) 0.04 m/s

Question

Determine the speed of the wave. A) 0.01 m/s B) 0.02 m/s C) 0.03 m/s D) 0.04 m/s E) 0.05 m/s A person was talking in a small room; and the sound intensity level is 60 dB everywhere in the room. Now, there are eight people talking in similar manner simultaneously in the room, what is the sound intensity level? (a) 60 dB (b) 79 dB (c) 74 dB (d) 64 dB (e) 69 dB Two loudspeakers, A and B, are separated by a distance of 2.0 m. The speakers emit sound waves at a frequency of 680 Hz that are exactly out of phase. The speed of is 343 m/s. How far from speaker A along the +x axis a point of constructive interference occur? A) 0.25 m B) 0.30 m C) 0.46 m D) 0.88 m

Explanation / Answer

Speed of sound v = 343 m/s

Frequency of sound f = 680 Hz

Thus, wavelength w = v/f = 0.5044 m

For constructive interference, path difference should be multiple of wavelength or 360' phase difference . As these sources are already completely out of phase, that means they are 180' out of phase, we need 180' more phase difference or path difference of wavelength/2

Thus, let the point of constructive interference is at distance x from A. So, it will be (2-x) from B.

Thus path difference between them is (2-x) - x

And this should be w/2 = 0.5044/2 = 0.2522

So, by equating these two, we get x = 0.88 m (D)

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