• # 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) ${{r}_{e}}>{{r}_{p}}={{r}_{He}}$

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