CET Karnataka Medical CET - Karnataka Medical Solved Paper-2007

  • 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 \[p=\sqrt{2mE}\] or \[\frac{{{p}_{p}}}{{{p}_{d}}}=\sqrt{\frac{{{m}_{p}}}{{{m}_{d}}}}\] ...(ii) From Eqs. (i) and (ii), we have, \[\frac{{{r}_{p}}}{{{r}_{d}}}=\sqrt{\frac{{{m}_{p}}}{{{m}_{d}}}}=\sqrt{\frac{1}{2}}=\frac{1}{\sqrt{2}}\]


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