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A string is fastened tightly between two walls 24cm apart...

A string is fastened tightly between two walls 24cm apart. The wavelength of the second overtone is

A.

24cm

B.

16cm

C.

12cm

D.

8cm

Correct answer is B

For a string fixed at both ends and plucked at the middle, the fundamental frequency is given
by f0 = v/λ, where v = velocity of sound, λ = wave length.
At its fundamental, note, the the length of the string is given l = λ/2, => λ0 = 2l, where λ0 = wave length fundamental note. for the first over tone, λ1 = l.
For the second over tone, λ2 = 21/3 = (2 x 24)/3 = 16cm.

i.e. λ2 = 16cm.