NEET Physics Wave Mechanics NEET PYQ-Wave Mechanics

  • question_answer
    The phase difference between two waves, represented by                      [AIPMT (S) 2004]
    \[{{y}_{1}}={{10}^{-6}}\sin [100t+(x/50)+0.5]\,m\]
    \[{{y}_{2}}={{10}^{-6}}\cos [100t+(x/50)]\,m\]
    where x is expressed in metres and t is expressed in seconds, is approximately:

    A)  1.07 rad

    B)                   2.07 rad          

    C)  0.5 rad  

    D)        1.5 rad

    Correct Answer: A

    Solution :

    The given waves are
    \[{{y}_{1}}={{10}^{-6}}\sin [100t+(x/50)+0.5]m\]
    and       \[{{y}_{2}}={{10}^{-6}}\cos [100t+(x/50)]\,\,m\]
    \[\Rightarrow \]   \[{{y}_{2}}={{10}^{-6}}\sin \,[100t+(x/50)+\frac{\pi }{2}]\,\,m\]
                \[\left[ \because \sin \left( \frac{\pi }{2}+\theta  \right)=\cos \theta  \right]\]  
    Hence, the phase difference between the waves is
                \[\Delta \phi =\left( \frac{\pi }{2}-0.5 \right)rad\]
                \[=\left( \frac{3.14}{2}-0.5 \right)\,\,rad\]
                \[=(1.57-0.5)\,\,rad\]
                \[=(1.07)\,\,rad\]
    Note:    The given waves are sine and cosine function, so they are plane progressive harmonic waves.


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