Magnetics 1 Question 20
20. An electron and a proton are moving on straight parallel paths with same velocity. They enter a semi-infinite region of uniform magnetic field perpendicular to the velocity. Which of the following statement(s) is/are true?
(2011)
(a) They will never come out of the magnetic field region
(b) They will come out travelling along parallel paths
(c) They will come out at the same time
(d) They will come out at different times
Show Answer
Answer:
Correct Answer: 20. (b, d)
Solution:
$$ \begin{array}{rlrl} r= & \frac{m v}{B q} \text { or } & r & \propto m \\ \therefore & & r _e<r _p \text { as } m _e<m _p \\ & \text { Further, } & T & =\frac{2 \pi m}{B q} \end{array} $$
or
$\therefore T _e<T _p, t _e=\frac{T _e}{2}$ and $t _p=\frac{T _p}{2}$ or $t _e<t _p$
