Q11. A proton and a deutron ( $q = + \mathrm { e } , m = 2.0 \mathrm { u }$ ) having same kinetic energies enter a region of uniform magnetic field $\vec { B }$, moving perpendicular to $\vec { B }$. The ratio of the radius $r _ { d }$ of deutron path to the radius $r _ { p }$ of the proton path is:\\
(1) $\sqrt { 2 } : 1$\\
(2) $1 : 1$\\
(3) $1 : \sqrt { 2 }$\\
(4) $1 : 2$