JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2007

  • question_answer
        A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is:

    A) \[E/c\]                 

    B) \[2E/c\]

    C) \[Ec\]                                   

    D) \[E/{{c}^{2}}\]

    Correct Answer: B

    Solution :

                    Initial momentum of surface \[{{p}_{i}}=\frac{E}{c}\] where\[c=\]velocity of light (constant). Since, the surface is perfectly reflecting, so the same momentum will be reflected completely Final momentum \[{{p}_{f}}=\frac{E}{c}\]      (negative value) \[\therefore \]Change in momentum \[\Delta p={{p}_{f}}-{{p}_{i}}=-\frac{E}{c}-\frac{E}{c}=-\frac{2E}{c}\] Thus, momentum transferred to the surface is                 \[\Delta p=|\Delta p|=\frac{2E}{c}\]


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