An $\alpha$ particle and a proton are moving along the same direction with the same kinetic energy. They enter a uniform magnetic field acting perpendicular to their velocities. The ratio of radii of their paths is:

$2: 1$ $4: 1$ $1: \sqrt{2}$ $1: 1$

$1: 1$

The correct answer is Option (4) → $1: 1$