Discussion Forum



1)

An electron and a proton are moving on shaight 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?


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) Thev will come out at different times

Answer:

Option B,D

Explanation:

 $ r= \frac{mv}{Bq}$

 or   $ r \propto m$

 $\therefore$    $r_{e} <r_{p}$  as $m_{e}< m_{p}$

 Further  , $T = \frac{2 \pi m}{Bq}$

 or  $ T \propto m$

28112021727_t1.PNG

 $\therefore$   $T_{e} <T_{p}$

 $t_{e} = \frac{ T_{e}}{2}$

 and $t_{p}=\frac{ T_{P}}{2}$

 or   $ t_{e}  < t_{p}$

 $\therefore$   Correct options are (b) and (d) 

 

Note In JEE 2011, official answer key' correct oPtions were given bc, bd, bcd, here student should realise that both the electron and Proton enter the magnetic field at the same time or at different times

Analysis of Question
(i) Question is simPle'
(ii) In the situation given above particle
will never complete the circle unless
the magnetic field is all around