Magnetics 1 Question 9
9. An electron moving with a speed $u$ along the positive $x$-axis at $y=0$ enters a region of uniform magnetic field $\mathbf{B}=-B _0 \hat{\mathbf{k}}$ which exists to the right of $y$-axis. The electron exits from the region after sometime with the speed $v$ at coordinate $y$, then
(2004, 2M)
(a) $v>u, y<0$
(b) $v=u, y>0$
(c) $v>u, y>0$
(d) $v=u, y<0$
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Answer:
Correct Answer: 9. (d)
Solution:
- Magnetic force does not change the speed of charged particle. Hence, $v=u$. Further magnetic field on the electron in the given condition is along negative $y$-axis in the starting. Or it describes a circular path in clockwise direction. Hence, when it exits from the field, $y<0$.
