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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2010

  • question_answer
      Red light of wavelength 625 nm is incident normally on an optical diffraction grating with \[2\times {{10}^{5}}\] lines/m. Including central principal maxima, how many maxima may be observed on a screen which is far from the grating?  

    A) 15

    B) 17

    C) 8

    D) 16

    Correct Answer: B

    Solution :

      For principal maxima in grating spectra                   \[\frac{\sin \theta }{N}=n\lambda \]   where, \[n=(1,\,\,2,\,\,3)\] is the order of principal maxima and \[\theta \] is the angle of diffraction.                   \[n=\frac{1}{\lambda N}=\frac{1}{6.25\times {{10}^{-7}}\times 2\times {{10}^{5}}}=8\]   \[\therefore \] Number of maxima \[=2n+1=2\times 8+1=17\]  


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