NEET Sample Paper NEET Sample Test Paper-5

  • question_answer
    A proton of mass m and charge \[+e\] is moving in a circular orbit in a magnetic field with energy \[1\,meV\]. What should be the energy of \[\alpha \] -particle (mass Am and charge \[=+2e\]), so that it can revolve in the path of same radius?

    A)  \[1meV\]            

    B)  \[4meV\]

    C)  \[4meV\]                    

    D)  \[0.5meV\]

    Correct Answer: A

    Solution :

    As        \[r=\frac{\sqrt{2mK}}{qB}\] \[\Rightarrow \]               \[K\propto \frac{{{q}^{2}}}{m}\] Suppose the values of K for photon and a-particle are \[{{K}_{P}}\] and \[{{K}_{\alpha }},\] respectively. Then,         \[\frac{{{K}_{P}}}{{{K}_{\alpha }}}={{\left( \frac{{{q}_{p}}}{{{q}_{\alpha }}} \right)}^{2}}\times \frac{{{m}_{\alpha }}}{{{m}_{p}}}\] \[\Rightarrow \]               \[\frac{{{K}_{p}}}{{{K}_{\alpha }}}={{\left( \frac{{{q}_{p}}}{2{{q}_{p}}} \right)}^{2}}\times \frac{4{{m}_{p}}}{{{m}_{p}}}=1\] \[\Rightarrow \]               \[{{K}_{\alpha }}=1meV\]         


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