BHU PMT BHU PMT (Screening) Solved Paper-2008

  • question_answer
    A proton, a deuteron and an\[\alpha -\]particle with the same KE enter a region of uniform magnetic field, moving at right angles to B. What is the ratio of the radii of their circular paths?

    A)  \[1:\sqrt{2}:1\]

    B)  \[1:\sqrt{2}:\sqrt{2}\]

    C)  \[\sqrt{2}:1:1\]                

    D)  \[\sqrt{2}:\sqrt{2}:1\]

    Correct Answer: A

    Solution :

                     At right angles to magnetic field, charged particles acquire circular path at which magnetic force provides necessary centripetal force to keep it moving on circular path. ie,           \[qvB=\frac{m{{v}^{2}}}{r}\] \[\therefore \]  \[r=\frac{mv}{qB}=\sqrt{\frac{2mE}{{{q}^{2}}{{B}^{2}}}}\] where\[E=KE\]of particle                 \[{{r}_{p}}=\sqrt{\frac{2mE}{{{e}^{2}}{{B}^{2}}}},\] \[{{r}_{d}}=\sqrt{\frac{2\times 2m\times E}{{{e}^{2}}{{B}^{2}}}}\] and        \[{{r}_{\alpha }}=\sqrt{\frac{2\times 4m\times E}{{{(2e)}^{2}}{{B}^{2}}}}\] \[\therefore \]  \[{{r}_{p}}:{{r}_{d}}:{{r}_{\alpha }}=1:\sqrt{2}:1\]             


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