MGIMS WARDHA MGIMS WARDHA Solved Paper-2008

  • question_answer
    A proton and a deuteron with the same initial kinetic energy enter a magnetic field in a direction perpendicular to the direction of the field. The ratio of the radii of the circular trajectories described by them is

    A) 1 : 4 

    B) \[1:\sqrt{2}\]

    C) 1 : 1                                       

    D) 1 : 2

    Correct Answer: B

    Solution :

    For a moving charge in a perpendicular magnetic field, \[\frac{m{{v}^{2}}}{r}=Bqv\] \[\Rightarrow \]               \[r=\frac{mv}{Bq}\]                 \[=\frac{p}{Bq}\] Or           \[\frac{{{r}_{p}}}{{{r}_{d}}}=\frac{{{P}_{p}}}{{{P}_{d}}}\]                                   ...(i) (as q is same for both) Also, momentum\[P=\sqrt{2\,mE}\] Or           \[\frac{{{P}_{p}}}{{{P}_{d}}}=\sqrt{\frac{{{m}_{p}}}{{{m}_{d}}}}\]                             ??(ii) From Eqs. (i) and (ii), we have, \[\frac{{{r}_{p}}}{{{p}_{d}}}=\sqrt{\frac{{{m}_{p}}}{{{m}_{d}}}}=\sqrt{\frac{1}{2}}=\frac{1}{\sqrt{2}}\]


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