A charged particle is set free from rest in a region where constant, uniform electric and magnetic fields exist and both fields point in the same direction. The particle will move along a

helical path
straight path
elliptical path
circular path

Correct answer: straight path

Solution

The charge starts at rest, so qE accelerates it along E, which is parallel to B. Its velocity stays parallel to B, making qv x B = 0 at all times. It therefore moves in a straight line.

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