Wave Motion 4 Question 25

2. The correct figure that shows schematically, the wave pattern produced by superposition of two waves of frequencies $9 Hz$ and $11 Hz$, is

(2019 Main, 10 April II)

(a)

(b)

(c)

(d) 0

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Answer:

Correct Answer: 2. (a)

Solution:

  1. When waves of nearby frequencies overlaps, beats are produced.

Beat frequency is given by, $f _{\text {beat }}=f _1-f _2$

Here, $f _1=11 Hz$ and $f _2=9 Hz$ $\Rightarrow$ Beat frequency is, $f _{\text {beat }}=11-9=2 Hz$

Hence, time period of beats or time interval between beats, $T=\frac{1}{f _{\text {beat }}} \Rightarrow T=\frac{1}{2}=0.5 s$

So, resultant wave has a time period of $0.5 s$ which is correctly depicted in option (a) only.



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