Question

An electron moving with a speed u along the positive x-axis at y = 0 enters a region of uniform magnetic field $B=-B_0 k$ which exists to the right of v-axis. The electron exits from the region after sometime with the speed v at coordinate y, then

• A. v > u, y < 0
• B. v = u, y > 0
• C. v > u, y > 0
• D. v = u, y < 0

Answer 1

Answer: (D)

v = u, y < 0

Answer 2

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