BCECE Medical BCECE Medical Solved Papers-2003

  • question_answer
    \[{{H}^{+}},H{{e}^{2+}}\] and \[{{O}^{2-}}\] all having the same kinetic energy pass through a region in which there is a uniform magnetic field perpendicular to their velocity. The masses of \[{{H}^{+}},H{{e}^{2+}}\] and \[{{O}^{2-}}\] are 1 amu, 4 amu and 16 amu, respectively. Then:

    A)  \[{{H}^{+}}\] will be deflected most

    B)  \[{{O}^{2-}}\]will be deflected most

    C)  \[H{{e}^{2+}}\] and \[{{O}^{2-}}\] will be deflected most

    D)  all will be deflected most

    Correct Answer: A

    Solution :

    When a charged particle enters magnetic field perpendicularly, then it moves on circular path under magnetic force providing centripetal force. Magnetic force = centripetal force i.e., \[Bqv=\frac{m{{v}^{2}}}{r}\] or \[r=\frac{mv}{Bq}\] But \[E=\frac{1}{2}m{{v}^{2}}={{p}^{2}}/2m\] \[\therefore \] \[r=\frac{\sqrt{2\,mE}}{Bq}\] or \[r\propto \frac{\sqrt{m}}{q}\] \[\therefore \] \[{{r}_{{{H}^{+}}}}+:{{r}_{H{{e}^{2r}}}}:{{r}_{{{O}^{2-}}}}=\frac{\sqrt{m}}{e}:\frac{\sqrt{4m}}{e}:\frac{\sqrt{16m}}{2\,e}\] Thus, \[H{{e}^{2+}}\] and \[{{O}^{2-}}\]are deflected equally while \[{{H}^{+}}\] is deflected most


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