Physics-
General
Easy
Question
An electron moving with a speed u along the positive x-axis at y = 0 enters a region of uniform magnetic field 
which exists to the right of y-axis. The electron exits from the region after some time with the speed v at co-ordinate y, then
- v > u, y < 0
- v = u, y > 0
- v > u, y > 0
- v = u, y < 0
The correct answer is: v = u, y < 0
The energy of a charged particle moving in magnetic field remains constant because the magnetic field does not do any work. Therefore kinetic energy is constant i.e. 
.
The force on electron will act along negative y-axis initially. The electron will undergo circular motion in clockwise direction and emerge out the field. So 
.
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