Q. In Thomson mass spectrograph, singly and doubly ionised particles from similar parabola corresponding to magnetic fields of 0.8 T and 1.2 T for a constant electric field. The ratio of masses f ionised particles will be
A) 3 : 8
B) 2 : 9
C) 8 : 3
D) 9 : 2
Explanation
(b) For similar parabola; $y^{2} = \frac{B^{2}lD}{E}\frac{q}{m}x$, will be same for two particles. It means $\frac{B^{2}q}{m} =$ a constant for these two particles.
$\therefore\ \frac{m_{1}}{m_{2}} = \frac{B_{1}^{2}q_{1}}{B_{2}^{2}q_{2}} = \left( \frac{0.8}{1.2} \right)^{2} \times \frac{e}{2e} = \frac{2}{9}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.