Uttarakhand PMT Uttarakhand PMT Solved Paper-2006

  • question_answer
    Equations of motion in the same direction are given by: \[{{y}_{1}}=2a\sin (\omega t-kx)\] \[{{y}_{2}}=2a\sin (\omega t-kx-\text{ }\!\!\theta\!\!\text{ })\] The amplitude of the medium particle will be:

    A)  \[2a\sin \text{ }\!\!\theta\!\!\text{ }\]         

    B)  \[\sqrt{2}a\sin \text{ }\!\!\theta\!\!\text{ }\]

    C)  \[4a\sin \frac{\text{ }\!\!\theta\!\!\text{ }}{2}\]         

    D)  \[\sqrt{2}a\sin \frac{\text{ }\!\!\theta\!\!\text{ }}{2}\]

    Correct Answer: C

    Solution :

     The given equations of motion are \[{{y}_{1}}=2a\sin (\omega t-kx)\] \[{{y}_{2}}=2a\sin (\omega t-kx-\theta )\] Now, the resultant equation of wave is given by \[y={{y}_{1}}+{{y}_{2}}\] \[=2a\sin (\omega t-kx)+2a\sin (\omega t-kx-\theta )\] \[y=2a\left[ 2\sin \frac{(\omega t-kx-\omega t-kx-\theta )}{2} \right.\]           \[\left. \times \cos \frac{\omega t-kx-(\omega t-kx-\theta )}{2} \right]\] \[y=4a\cos \frac{\theta }{2}\sin \left( \omega t-kx-\frac{\theta }{2} \right)\] ?.(1) Now, comparing Eq. (1) with\[y=A\sin (\omega t-kx),\]we have Resultant amplitude \[A=4a\cos \frac{\theta }{2}\]


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