When a moving proton is subjected to a uniform magnetic field it produces 5 revolutions in $25\mu s.$ what will be the time period of revolution for a moving $\alpha$ -particle subjected to the same magnetic field.

$10\mu s$

$ \text{Time period of revolution for proton }T = \frac{2\pi m}{qB} = 5\mu s $

$ \text{Time Period For an } \alpha \text{ paticle is }T'= \frac{2\pi 4m}{2qB} = \frac{4\pi m}{qB} = 2T = 10\mu s  $