In the figure shown, a charged particle of mass 2 g and charge `5 mu C` enters a circular region of radius `10 cm`, in which there is a uniform magnetic field of strength 4 T and directed perpendicular to the plane of circular region in the figure. If the particle velocity vector rotates through `90^(@)` angle in passing through this region then its period is :

Options

A. 0.25 mm/s
B. 4 mm/s
C. 1 cm/s
D. 1 mm/s

Answer

D

Explanation

The particle will move along a circle of radius equal to be radius of circular region in which magnetic field is present (See in fig)
From `R =(mv)/(qB),v=(qBR)/(m)`
`=(5xx10^(-6)xx4xx(0.1))/(2xx10^(-3))=10^(-3)m//s=1 mm//s`