JCECE Engineering JCECE Engineering Solved Paper-2013

  • question_answer
    Two coherent sources of intensity ratio \[\beta \] interfere. Then, the value\[({{I}_{\max }}-{{I}_{\min }})/\]\[({{I}_{\max }}+{{I}_{\min }})\] is

    A) \[\frac{1+\beta }{\sqrt{\beta }}\]                            

    B) \[\sqrt{\frac{1+\beta }{\beta }}\]

    C) \[\frac{1+\beta }{2\sqrt{\beta }}\]                          

    D)  \[\frac{2\sqrt{\beta }}{1+\beta }\]

    Correct Answer: D

    Solution :

    Given,\[\frac{{{I}_{1}}}{{{I}_{2}}}=\beta =\frac{{{a}^{2}}}{{{b}^{2}}}\] \[\Rightarrow \]               \[\frac{a}{b}=\sqrt{\beta }\]                 \[{{I}_{\max }}={{(a+b)}^{2}}\] and        \[{{I}_{\min }}={{(a-b)}^{2}}\] \[\therefore \]  \[\frac{{{I}_{\max }}-{{I}_{\min }}}{{{I}_{\max }}+{{I}_{\min }}}=\frac{{{(a+b)}^{2}}-{{(a-b)}^{2}}}{{{(a+b)}^{2}}+{{(a-b)}^{2}}}\]                 \[=\frac{4ab}{2({{a}^{2}}+{{b}^{2}})}=\frac{2ab}{({{a}^{2}}+{{b}^{2}})}\]                 \[=\frac{2b\cdot b\sqrt{\beta }}{{{b}^{2}}+\beta {{b}^{2}}}=\frac{2\sqrt{\beta }}{1+\beta }\]


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