1) A loudspeaker produces a sound level (loudness) of 40 dB at some distance. Wh

Question

1) A loudspeaker produces a sound level (loudness) of 40 dB at some distance. What would be the new sounds level (loudness) produced by 20 identical speakers at the same dstance?

A) 60db

B) 100dB

C) 90dB

D) 53dB

E) 800dB

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2) An organ pipe OPEN AT BOTH ENDS is resnated (stading wave) with second harmonic frequency of 686 Hz. The speed of sound in air is 343 m/s. The length of the pipe is:

A) 10 cm

B) 25 cm

C) 30 cm

d) 50 cm

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3) The four strings of a musical instrument are all made of the same material, sae length and are under the same tension, but have different thickness. Waves travel:

Ans: Faster on the thinnest string.

Why?

Explanation / Answer

1.The difference in decibels between the two is

L2-L1=10 log (P2/P1) dB, where the log is to base 10

L2-40=10 log(20P1/P1)

         = 10 log(20)

         = 10*1.3010

         = 13.010

   L2=40+13.010=53.010 DB

2. When the pipe is open at both the ends the resonant frequencies are v/2l, 2(v/2l), 3(v/2l)......

Therefore f=2(v/2l)=v/l

l=v/f=343/686=1/2=0.5m

3. Velocity of sound wave in a string with Tension T, Mass M is v=sqrt(T/M)

As the tensions is same, Velocity inversily proportional to sqrt of mass. So, Thinner wire will have less mass thats why velocity is more

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