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Question
An electron is moving along the positive x-axis. You want to apply a magnetic field for a short time so that the electron may reverse its direction and move parallel to the negative x-axis. This can be done by applying the magnetic field along
(a) y-axis
(b) z-axis
(c) y-axis only
(d) z-axis only
Solution
(a) y-axis
(b) z-axis
Any magnetic field, except one parallel to the direction of velocity can change the direction of the particle. Therefore, either the magnetic field along y-axis or along z-axis can reverse the direction of the particle, as the velocity is along the x direction
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