Q.Two point charges A = +5.0 $\mu C$ and B = -5.0 $\mu C$ are separated by 5.0 cm. A point charge C = 1.0 $\mu C$ is placed at 3.0 cm away from the centre on the perpendicular bisector of the line joining the two point charges. The charge at C will experience a force directed towards (A) point A (B) point B (C) a direction parallel to line AB (D) a direction along the perpendicular bisector

[!TLDR] On the perpendicular bisector of a +/- charge pair, the net field points from the positive charge toward the negative charge -- so the force …

Charge C is placed on the PERPENDICULAR BISECTOR of the line joining A (+5.0 $\mu C$) and B (-5.0 $\mu C$) -- this is exactly the equatorial-line geometry of an electric dipole (section 10.9.2, Case 2), with A and B playing the roles of the dipole's positive and negative charges respectively. As derived there, the net electric field at any point on a dipole's equatorial line points ANTI-PARALLEL to the dipole moment $\vec{p}$ -- that is, from the region NEAR the positive charge toward the region NEAR the negative charge. Since the dipole moment here points from B (negative) to A (positive), the net field at C's location points from A toward B. Charge C is positive (+1.0 $\mu C$), so the FORCE on it, $\vec{F}=q_C\vec{E}$, points in the SAME direction as this net field -- that is, d …

Recognise the A(+)/B(-) pair as an electric dipole and C's position on their perpendicular bisector as the dipole's equatorial line, then apply the known equatorial-f …

Assuming the field at an equatorial point is directed ALONG the dipole moment (the axial-point rule) rather than anti-parallel to it (the correct e …