JCECE Engineering JCECE Engineering Solved Paper-2006

  • question_answer
    If the intensity of fringe at wavelength\[\lambda \]is\[K\], then its intensity at wavelength \[\lambda /2\] is:

    A) \[\frac{K}{2}\]                                  

    B) \[K\]

    C)  \[zero\]                                              

    D)  \[\sqrt{2}K\]

    Correct Answer: C

    Solution :

    Key Idea: Resultant intensity is given by                 \[{{I}_{R}}={{I}_{1}}+{{I}_{2}}+2\sqrt{{{I}_{1}}{{I}_{2}}}\cos \phi \] Resultant intensity due to two waves of intensities \[{{I}_{1}},\,\,{{I}_{2}}\] is given by                 \[{{I}_{R}}={{I}_{1}}+{{I}_{2}}+2\sqrt{{{I}_{1}}{{I}_{2}}}\cos \phi \] when path difference is\[\lambda ,\,\,\phi =2\pi \] when path difference is\[\frac{\lambda }{2},\,\,\phi =\pi \] \[\therefore \]  \[{{I}_{{{R}_{1}}}}=I+I+2I\cos 2\pi \]                 \[{{I}_{{{R}_{1}}}}=4I=K\]                 \[{{I}_{{{R}_{2}}}}=I+I+2I\cos \pi \]                 \[{{I}_{{{R}_{2}}}}=0\]


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