BCECE Medical BCECE Medical Solved Papers-2014

  • question_answer Light with an energy flux of 18 \[W/c{{m}^{2}}\] falls on a non-reflecting surface at normal incidence. The surface has an area of 20 \[c{{m}^{2}}\], then the total momentum delivered on the surface during a span of 30 min is

    A)  \[2.16\times {{10}^{-3}}kg-m/s\]

    B)  \[1.52\times {{10}^{-5}}kg-m/s\]

    C)  \[8.31\times {{10}^{-8}}kg-m/s\]  

    D)  \[18.2\times {{10}^{-6}}kg-m/s\]

    Correct Answer: A

    Solution :

    Total energy falling \[U=(18\,W/c{{m}^{2}})\,(30\times 60s)\,(20c{{m}^{2}})\] \[=6.18\times {{10}^{5}}J\] Total, momentum delivered is \[P=\frac{U}{c}=\frac{6.48\times {{10}^{5}}}{3\times {{10}^{8}}}=2.16\times {{10}^{-3}}kg-m/s\]

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