Wave Motion 2 Question 2

2. A string 2.0m long and fixed at its ends is driven by a 240Hz vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is

(Main 2019, 9 April II)

(a) 180m/s,80Hz

(b) 320m/s,80Hz

(c) 320m/s,120Hz

(d) 180m/s,120Hz

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Answer:

Correct Answer: 2. (b)

Solution:

  1. Frequency of vibration of a string in nth harmonic is given by

fn=nv2l

where, v= speed of sound and l= length of string.

Here, f3=240Hz,l=2m and n=3

Substituting these values in Eq. (i), we get

240=3×v2×2v=4×2403=320ms1

Also, fundamental frequency is

f=fnn=f33=2403=80Hz



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