J & K CET Medical J & K - CET Medical Solved Paper-2012

  • question_answer
    An electron and a proton, both having the same kinetic energy, enter a region of uniform magnetic field, in a plane perpendicular to the field. If their masses are denoted by\[{{m}_{e}}\]and\[{{m}_{p}}\] respectively, then the ratio of the radii (electron to proton) of their circular orbits is

    A)  \[\sqrt{\frac{{{m}_{p}}}{{{m}_{e}}}}\]

    B)  \[\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\]

    C)  \[\frac{{{m}_{e}}}{{{m}_{p}}}\]

    D)  \[1\]

    Correct Answer: B

    Solution :

     Radius of circular path in a uniform magnetic field \[r=\frac{mv}{qB}\] Kinetic energy of the charged-particle \[K=\frac{1}{2}m{{v}^{2}}\] \[{{v}^{2}}=\frac{2K}{m}\] \[\Rightarrow \] \[v=\sqrt{\frac{2K}{m}}\] \[\therefore \] \[r=\frac{m}{qB}\sqrt{\frac{2K}{m}}\] \[r=\frac{\sqrt{2Km}}{qB}\] For the same value of\[K\]and B \[r\propto \frac{\sqrt{m}}{q}\] \[\therefore \] \[\frac{{{r}_{e}}}{{{r}_{p}}}=\frac{\sqrt{{{m}_{e}}}}{\sqrt{{{m}_{p}}}}\times \frac{{{q}_{p}}}{{{q}_{e}}}\] \[\frac{{{r}_{e}}}{{{r}_{p}}}=\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\times \frac{e}{e}=\sqrt{\frac{{{m}_{e}}}{{{m}_{p}}}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner