question_answer

An electron is moving along positive x-axis. To get it moving on an anticlockwise circular path in x-y plane, a magnetic filed is applied                                                            [MP PMT 1999]

A)            Along positive y-axis         

B)            Along positive z-axis

C)            Along negative y-axis       

D)            Along negative z-axis

Correct Answer: B

Solution :

                   To move the electron in xy plane, force on it must be acting in the y-direction initially. The direction of \[\vec{F}\]is known, and the direction of v is known, hence by applying Fleming's left hand rule, the direction of magnetic field is also determined.