A. 40Hz, 80Hz, 120Hz
B. 80Hz, 160Hz, 240Hz
C. 180Hz, 360Hz, 540Hz
D. 369Hz, 180Hz, 90Hz

Correct Answer:

Option A – 40Hz, 80Hz, 120Hz

Explanation

In vibrations in string, the fundamental frequency happens to be the first harmonic, and is given as

f0 = V/2l.

Where V = Velocity of the sound wave, I = Length of the string.

The second harmonic is the first overtone given by

f1 = V/l = 2f0 ;

and the third harmonic happens to be the second overtone, given by

f2 = 3V/2l = 2f0.

Thus if V = 120m/s and l = 1.5m
Thus f1 = 2f0 = 2 x 40 = 80Hz
Thus f2 = 3f0 = 3 x 40 = 120Hz
Thus we have in order, 40Hz, 80Hz, 120Hz

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