JEE Main & Advanced JEE Main Paper (Held on 10-4-2019 Morning)

  • question_answer A proton, an electron, and a Helium nucleus, have the same energy. They are in circular orbits in a plane due to magnetic field perpendicular to the plane. Let \[{{r}_{p}},{{r}_{e}}\]and \[{{r}_{He}}\] be their respective radii, then, [JEE Main 10-4-2019 Morning]

    A) \[{{r}_{e}}>{{r}_{p}}>{{r}_{He}}\]      

    B) \[{{r}_{e}}<{{r}_{p}}<{{r}_{He}}\]

    C) \[{{r}_{e}}<{{r}_{p}}={{r}_{He}}\]      

    D) \[{{r}_{e}}>{{r}_{p}}={{r}_{He}}\]

    Correct Answer: C

    Solution :

    \[r=\frac{m\text{v}}{qB}=\frac{\sqrt{2mK}}{qB}\] \[{{r}_{He}}={{r}_{p}}>{{r}_{e}}\]      

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