What is the direction of the electric field at a point on the equatorial line of an electric dipole?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → opposite to the dipole moment
At a point on the equatorial line, the two charges of the dipole are at equal distances. So their fields have equal size. The parts of these fields normal to the dipole axis cancel, and the parts along the axis add. At large distances, \( \vec{E}=-\frac{\vec{p}}{4\pi\varepsilon_0 r^3} \).
Option (1) in the direction of the dipole moment — Incorrect. The field is along the dipole axis, but it points from \( +q \) towards \( -q \). This is against \( \vec{p} \), which points from \( -q \) to \( +q \).
Option (2) perpendicular to the dipole axis — Incorrect. The components normal to the dipole axis cancel each other. So no field is left in this direction.
Option (3) away from the dipole — Incorrect. A field pointing away from the dipole would lie along the equatorial line. These components of the two fields cancel.
Option (4) opposite to the dipole moment — Correct. The field is parallel to the dipole axis and points opposite to \( \vec{p} \). The minus sign in \( \vec{E}=-\frac{\vec{p}}{4\pi\varepsilon_0 r^3} \) shows this.
NCERT (2026-27):
The field of an electric dipole – “… Clearly, the components normal to the dipole axis cancel away. The components along the dipole axis add up. The total electric field is opposite to p̂. …”