Q. An $\alpha$-particle with a specific charge of $2.5 \times 10^{7}\ C\ {kg}^{- 1}$ moves with a speed of $2 \times 10^{5}\ {ms}^{- 1}$ in a perpendicular magnetic field of 0.05 T. Then the radius of the circular path described by it is

A) 8 cm
B) 4 cm
C) 16 cm
D) 2 cm
Explanation

(c) $\ \ \ \ \ \ \ \ r = \frac{mv}{Bq}$
$\Rightarrow \ \ r = \frac{v}{B\frac{q}{m}} = \frac{2 \times 10^{5}}{0.05 \times 2.5 \times 10^{7}}$
$\ \ \ \ \ \ \ \ \ \ = \frac{2 \times 10^{7}}{12.5 \times 10^{7}} = \frac{200}{12.5}\ cm = 16\ cm$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.