Question

Two point charges +q and -q are held fixed at (-d, 0) and (d, 0) respectively of a x - y coordinate system. Then :

• A. The electric field E at all points on the axis has the same direction
• B. Work has to be done in bringing a test charge from $\infty$ to the orgin
• C. Electric field at all points on y-axis is along x-axis
• D. The dipole moment is 2qd along the x-axis

Answer 1

The correct option is C Electric field at all points on y-axis is along x-axis

If we take a point M on the X-axis as shown in the figure, then the net electric field is in X-direction.

∴ Option (a) is incorrect.

If we take a point N on Y-axis, we find net electric field along +X direction. The same will be true for any point on X-axis.

So, (c) is a correct option.

The work is calculated as:

$W_{\infty to0}=q(V_{\infty }-V_0)=q(0-0)=0$

(b) is incorrect.

The direction of the dipole moment is from-:-ve to +ve and it is not along the X-axis. Therefore (d) is incorrect.