Manipal Engineering Manipal Engineering Solved Paper-2011

  • question_answer
    The rest energy of an electron is 0.511 MeV. The electron is accelerated from rest to a velocity 0.5 c. The change in its energy will he

    A)  0.026 MeV       

    B)         0.051 MeV

    C)  0.079 MeV       

    D)         0.105 MeV

    Correct Answer: C

    Solution :

    According to Einsteins equation relation between rest energy and moving energy is                 \[E={{E}_{0}}{{\left( 1-\frac{{{v}^{2}}}{{{c}^{2}}} \right)}^{-1/2}}\] Given,   \[v=0.5\,\,c\] \[\therefore \]  \[E={{E}_{0}}{{\left( 1-\frac{{{(0.5c)}^{2}}}{{{c}^{2}}} \right)}^{-1/2}}\]                 \[E={{E}_{0}}{{(1-0.25)}^{-1/2}}\]                 \[=\frac{{{E}_{0}}}{\sqrt{0.75}}\] Change in energy\[\Delta E=E-{{E}_{0}}\]                 \[=\frac{{{E}_{0}}}{\sqrt{0.75}}-{{E}_{0}}\]                 \[={{E}_{0}}\left( \frac{1}{\sqrt{0.75}}-7 \right)\]                 \[=0.511\left( \frac{1}{\sqrt{0.75}}-1 \right)\]                 \[=0.079\,\,MeV\]


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