JEE Main & Advanced Physics Mathematical Tools, Units & Dimensions Question Bank Self Evaluation Test - Physical World, Units and Measurements

  • question_answer
    Intensity observed in an interference pattern is \[I={{I}_{0}}Si{{n}^{2}}\]. \[At\theta ={{30}^{o}}\] intensity \[I=5\pm 0.0020W/{{m}^{2}}\]. Find percentage error in angle if \[{{I}_{0}}=20W/{{m}^{2}}\]                       

    A) \[\frac{4}{\pi }\sqrt{3}\times {{10}^{-2}}%\]   

    B)         \[\frac{2}{\pi }\sqrt{3}\times {{10}^{-2}}%\]

    C)  \[\frac{1}{\pi }\sqrt{3}\times {{10}^{-2}}%\]

    D)         \[\frac{3}{\pi }\sqrt{3}\times {{10}^{-2}}%\]

    Correct Answer: A

    Solution :

    [a] \[I={{I}_{0}}{{\sin }^{2}}\theta \Rightarrow \theta ={{\sin }^{-1}}\sqrt{\frac{I}{{{I}_{0}}}}\] \[d\theta =\frac{1}{2}\frac{\sqrt{{{I}_{0}}}}{\sqrt{{{I}_{0}}-I}}\frac{dI}{\sqrt{{{I}_{0}}\sqrt{I}}}\] \[\frac{d\theta }{\theta }=\frac{1}{2}\frac{dI}{\sqrt{I({{I}_{0}}-I)}\,{{\sin }^{-1}}\sqrt{I/{{I}_{0}}}}\] \[\therefore \,\,\,%\,error=\frac{4}{\pi }\sqrt{3}\times {{10}^{-2}}%\]


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