JEE Main & Advanced Sample Paper JEE Main - Mock Test - 44

  • question_answer
    When a wave travels in a medium, the particle displacement is given by the equation \[y=a\,\,sin\,2\pi \left( bt-cx \right)\] where a, b and c are constant. The maximum particle velocity will be twice the wave velocity if-

    A) \[c=\frac{1}{\pi a}\]      

    B)        \[c=\pi a\]

    C) \[b=ac\]

    D)        \[b=\frac{1}{ac}\]

    Correct Answer: A

    Solution :

    [a] Equation of the harmonic progressive wave given \[y=a\text{ }sin\,2\pi \left( bt-cx \right)\] Here \[2\pi v=\omega =2\pi b\Rightarrow v=b\] \[K=\frac{2\pi }{\lambda }=2\pi c\Rightarrow \frac{1}{\lambda }=c\] (here c is the symbol given for \[\frac{1}{\lambda }\] and not the velocity) \[\therefore \] Velocity of the wave \[=v\lambda =b\frac{1}{c}=\frac{b}{c}\] \[\frac{dy}{dt}=a2\pi b\text{ }cos2\pi \left( bt-cx \right)=a\omega cos(\omega t-kx)\] Maximum particle velocity \[=a\omega =a2\pi b=2\pi ab\] given this is \[2\times \frac{b}{c}\] i.e., \[2\pi a=\frac{2}{c}or\text{ c}=\frac{1}{\pi a}\]


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