KVPY Sample Paper KVPY Stream-SX Model Paper-1

  • question_answer
    The wavefront of a light beam is given by the equation \[x+2y+3z=c,\] (where c is arbitrary constant) then the angle made by the direction of light with the y-axis is:

    A) \[{{\cos }^{-1}}\frac{1}{\sqrt{14}}\]                

    B) \[{{\sin }^{-1}}\frac{2}{\sqrt{14}}\]

    C) \[{{\cos }^{-1}}\frac{2}{\sqrt{14}}\]    

    D) \[{{\sin }^{-1}}\frac{3}{\sqrt{14}}\]

    Correct Answer: C

    Solution :

    Here direction of light is given by normal vector\[\vec{n}=\hat{i}+2\hat{j}+3\hat{k}\] \[\therefore \] angle made by the \[\vec{n}\] with y-axis is given by \[\cos \beta =\frac{2}{\sqrt{{{1}^{2}}+{{2}^{2}}+{{3}^{2}}}}=\frac{2}{\sqrt{14}}\]  


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