JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank Motion of Charged Particle In Magnetic Field

  • question_answer
    A proton, a deuteron and an \[\alpha -\]particle having the same kinetic energy are moving in circular trajectories in a constant magnetic field. If \[{{r}_{p}},\,{{r}_{d}}\] and \[{{r}_{\alpha }}\] denote respectively the radii of the trajectories of these particles, then [IIT 1997 Re-Exam]

    A)            \[{{r}_{\alpha }}={{r}_{p}}<{{r}_{d}}\]                           

    B)            \[{{r}_{\alpha }}>{{r}_{d}}>{{r}_{p}}\]

    C)            \[{{r}_{\alpha }}={{r}_{d}}>{{r}_{p}}\]                           

    D)            \[{{r}_{p}}={{r}_{d}}={{r}_{\alpha }}\]

    Correct Answer: A

    Solution :

                       Given that \[{{K}_{p}}={{K}_{d}}={{K}_{\alpha }}\]= K (say) We know that mp = m, md = 2m and \[{{m}_{\alpha }}=4m\]and qp = e, qd = e and \[{{q}_{\alpha }}=2e\] Further\[r=\frac{\sqrt{2mK}}{qB}\]Þ\[{{r}_{p}}=\frac{\sqrt{2mK}}{eB}\], \[{{r}_{d}}=\frac{\sqrt{2\left( 2m \right)K}}{eB}=\sqrt{2}{{r}_{p}}\] and \[{{r}_{\alpha }}=\frac{\sqrt{2\left( 4m \right)K}}{\left( 2e \right)B}={{r}_{p}}\].  Hence \[{{r}_{\alpha }}={{r}_{p}}<{{r}_{d}}\]


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