Wave Motion 4 Question 2
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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Solution:
- 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.
