JEE Main & Advanced Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank Self Evaluation Test - Moving Charges and Mangetism

  • question_answer
    In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular path of radius R using a magnetic field B. If V and B are kept constant, the \[ratio\,\left( \frac{ch\operatorname{arge}\,on\,the\,ion}{mass\,of\,the\,ion} \right)\] will be proportional to

    A) \[1/{{R}^{2}}\]           

    B) \[{{R}^{2}}\]   

    C) R         

    D) \[1/R\]

    Correct Answer: A

    Solution :

    [a] In mass spectrometer, when ions are accelerated through potential V \[\frac{1}{2}m{{v}^{2}}=qV\]            ??.(i) As the magnetic field curves the path of the ions in a semicircular orbit \[Bqv=\frac{m{{v}^{2}}}{R}\Rightarrow v=\frac{BqR}{m}\]    ??..(ii) Substituting (ii) in (i) \[\frac{1}{2}m{{\left[ \frac{BqR}{m} \right]}^{2}}=qV\] or \[\frac{q}{m}=\frac{2V}{{{B}^{2}}{{R}^{2}}}\] Since F and B are constants, \[\therefore \,\,\frac{q}{m}\propto \frac{1}{{{R}^{2}}}\]


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