A proton, an electron, and a Helium nucleus, have the same energy. They are in circular orbitals in a plane due to magnetic field perpendicular to the plane. Let $r_p, r_e$ and $r_{He}$ be their respective radii, then
A$r_e > r_p = r_{He}$
B$r_e > r_p > r_{He}$
C$r_e < r_p < r_{He}$
D$r_e < r_p = r_{He}$
JEE MAIN 2019, Medium
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D$r_e < r_p = r_{He}$
d $r=\frac{m v}{q B}=\frac{\sqrt{2 m K}}{q B}$
$r_{\mathrm{He}}=r_{p}>r_{e}$
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