JEE Main & Advanced Physics Wave Mechanics Question Bank Stationary Waves

  • question_answer
    A wave represented by the given equation \[y=a\cos (kx-\omega \,t)\] is superposed with another wave to form a stationary wave such that the point x = 0 is a node. The equation for the other wave is                  [IIT 1988; MP PMT 1994, 97; AIIMS 1998; SCRA 1998; MP PET 2001; KCET 2001; AIEEE 2002; UPSEAT 2004]

    A)            \[y=a\sin (kx+\omega \,t)\]  

    B)            \[y=-a\cos (kx+\omega \,t)\]

    C)            \[y=-a\cos (kx-\omega \,t)\]

    D)            \[y=-a\sin (kx-\omega \,t)\]

    Correct Answer: B

    Solution :

                         Since the point \[x=0\] is a node and reflection is taking place from point \[x=0.\] This means that reflection must be taking place from the fixed end and hence the reflected ray must suffer an additional phase change of p or a path change of \[\frac{\lambda }{2}\]. So, if \[{{y}_{\text{incident}}}=a\cos (kx-\omega \,t)\] Þ \[{{y}_{\text{reflected}}}=a\cos (-kx-\omega \,t+\pi )\]\[=-a\cos (\omega \,t+kx)\]


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