Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2005

  • question_answer
      A proton and a deuteron both having the same kinetic energy, enter perpendicularly into a uniform magnetic field B. For motion of proton and deuteron on circular path of radius \[{{r}_{P}}\] and \[{{r}_{d}}\] respectively, the correct statement is

    A) \[{{r}_{d}}={{r}_{P}}\sqrt{2}\]                   

    B) \[{{r}_{d}}\frac{{{r}_{P}}}{\sqrt{2}}\]

    C) \[{{r}_{d}}={{r}_{P}}\]                                   

    D) \[{{r}_{d}}=2{{r}_{P}}\]

    Correct Answer: A

    Solution :

    Radius of circular path \[r=\frac{mv}{qB}\]           ??(i) and kinetic energy \[KE=\frac{1}{2}m{{v}^{2}}\] or \[v=\sqrt{\frac{2KE}{m}}\] putting the value of v in Eq. (i)                 \[r=\frac{m}{qB}\sqrt{\frac{2KE}{m}}=\frac{\sqrt{2m\,KE}}{qB}\]             ?..(ii) For proton \[{{(}_{1}}{{H}^{1}})\] and deuteron \[{{(}_{1}}{{H}^{2}})\] electronic charge are same and both have same kinetic energy. \[\therefore \] By Eq. (ii) \[r\propto \sqrt{m}\] or \[\frac{{{r}_{d}}}{{{r}_{p}}}=\sqrt{\frac{{{m}_{d}}}{{{m}_{p}}}}\] \[\because \]     \[{{m}_{d}}=2{{m}_{p}}\] \[\therefore \]  \[\frac{{{r}_{d}}}{{{r}_{p}}}=\sqrt{\frac{2{{m}_{p}}}{{{m}_{p}}}}\] \[\Rightarrow \]               \[{{r}_{d}}=\sqrt{2}{{r}_{p}}\]


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