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]

Question

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]

Smart Achievers · Accepted Answer

(2, 4)

The entry and exit of electron and proton in the magnetic field make the same angle with $A B$ as shown. Therefore both will come out travelling in parallel paths.

Also, $r = \frac{m v}{q B}$ or, $r \propto m$

$∵$ $m_{e} < m_{p}$ $∴$ $r_{e} < r_{p}$

and, $T = \frac{2 π m}{q B}$ or, $T \propto m$

$∴$ $T_{e} < T_{p},$ $t_{e} = \frac{T_{e}}{2}$ and $t_{p} = \frac{T_{p}}{2}$

or, $t_{e} < t_{p}$

Solution

Q.
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]

1 They will never come out of the magnetic field region.

2 They will come out travelling along parallel paths.

3 They will come out at the same time.

4 They will come out at different times.

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