JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank EM Waves

  • question_answer
    The intensity of gamma radiation from a given source is I. On passing through 36 mm of lead, it is reduced to \[\frac{I}{8}\]. The thickness of lead which will reduce the intensity to \[\frac{I}{2}\] will be [AIEEE 2005]

    A)             18 mm                                     

    B)             12 mm

    C)             6 mm                                        

    D)             9 mm

    Correct Answer: B

    Solution :

                       \[I'=I\,{{e}^{-\mu x}}\] Þ \[x=\frac{1}{\mu }{{\log }_{e}}\frac{I}{I\,'}\] (where I = original intensity, I' = changed intensity) \[36=\frac{1}{\mu }{{\log }_{e}}\frac{I}{I/8}\] = \[\frac{3}{\mu }{{\log }_{e}}2\]    ....(i) \[x=\frac{1}{\mu }{{\log }_{e}}\frac{I}{I/2}\] \[=\frac{1}{\mu }{{\log }_{e}}2\]       .....(ii)             From equation (i) and (ii),  \[x=12\,mm\].


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