question_answer

Four point +ve charges of same magnitude (Q) are placed at four corners of a rigid square frame as shown in figure. The plane of the frame is perpendicular to \[\]axis. If a ?ve point charge is placed at a distance z away from the above frame (z<<L) then                                                        [AIIMS 2005]

A)            ? ve charge oscillates along the \[\]axis.

B)            It moves away from the frame

C)            It moves slowly towards the frame and stays in the plane of the frame      

D)            It passes through the frame only once.

Correct Answer: A

Solution :

                     The negative charge oscillates, the resultant force acts as a restoring force and proportional to displacement. When it reaches the plane , the resultant force is zero and the mass moves down due to inertia. Thus oscillation is set.