question_answer

Two point charges \[+q\] and \[-q\] are held fixed at \[(-d,\,0)\] and \[(d,\,0)\] respectively of a \[(X,\,Y)\] coordinate system. Then  [IIT 1995]

A)                    E at all points on the \[Y-\]axis is along \[\hat{i}\]

B)                    The electric field \[\overrightarrow{E}\] at all points on the \[X-\]axis has the same direction

C)                    Dipole moment is \[2qd\] directed along \[\hat{i}\]

D)                    Work has to be done in bringing a test charge from infinity to the origin

Correct Answer: A

Solution :

           From figure, it is clear that \[\overrightarrow{E}\] at all points on the y-axis is along \[\hat{i}\]. Here \[\overrightarrow{E}\] of all points on x-axis cannot have the same direction. Here electric potential at origin is zero so no work is done in bringing a test charge from infinity to origin. Here dipole moment is in ? x direction (? q to +q). Hence only option (a) is correct.