question_answer

                A beam of electrons passes undetected through mutually perpendicular electric and magnetic fields. If the electric field is switched off, and the same magnetic field is maintained, the electrons move:

A)                                                                                                                                                                                             in an elliptical orbit                                        

B)                  in a circular orbit

C)                  along a parabolic path                  

D)                  along a straight line

Correct Answer: B

Solution :

                If both electric and magnetic fields are present and perpendicular to each other and the particle is moving perpendicular to both of                                 them with \[{{F}_{e}}={{F}_{m}}\]. In this situation\[\vec{E}\ne 0\]and \[B\ne 0\].                 But if electric field becomes zero, then only force due to magnetic field exists. Under this force, the charge moves along a circle.