NEET Sample Paper NEET Sample Test Paper-54

  • question_answer
    Two coherent sources of intensity ratio \[1\text{ }:\text{ }4\] produce an interference pattern. The fringe visibility will be-

    A) 1                                 

    B) 0.8

    C) 0.4                               

    D) 0.6

    Correct Answer: B

    Solution :

    \[V=\frac{{{\operatorname{I}}_{max}}\,-\,{{I}_{\min }}}{{{\operatorname{I}}_{max}}+{{I}_{\min }}}=\frac{\frac{{{\operatorname{I}}_{max}}}{{{I}_{\min }}}-1}{\frac{{{\operatorname{I}}_{max}}}{{{I}_{\min }}}+1}\] \[\frac{{{\operatorname{I}}_{max}}}{{{I}_{\min }}}={{\left( \frac{\frac{{{I}_{1}}}{{{I}_{2}}}+1}{\frac{{{I}_{1}}}{{{I}_{2}}}-1} \right)}^{2}}\] According to question \[\frac{{{I}_{1}}}{{{I}_{2}}}\,\,=\,\,\frac{1}{4}\]                                 ...(3) From eqs. (2) and (3) \[\frac{{{I}_{\max }}}{{{I}_{\min }}}\,\,=\,\,{{\left( \frac{\sqrt{\frac{1}{4}}+1}{\sqrt{\frac{1}{4}}-1} \right)}^{2}}\,\,=\,\,\frac{\frac{9}{4}}{\frac{1}{4}}\,\,=\,\,9\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,....(4)\] From eqs. (1) and (4) \[V=\frac{[9-1]}{[9+1]}\,\,=\,\frac{8}{10}\,\,=\,\,0.8\]


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