How many of the following statements about an electric dipole are correct?
(A) The total charge of an electric dipole is zero.
(B) The direction of a dipole is taken from its positive charge to its negative charge.
(C) Far away from a dipole, its electric field falls off as \(1/r^{3}\).
(D) At a given distance, the field of a dipole has the same magnitude in all directions.
(E) In a uniform electric field, the net force on a dipole is zero.
(F) A \(\mathrm{CO_2}\) molecule has a permanent dipole moment.
(G) In a uniform electric field, the torque on a dipole is zero when its dipole moment is along the field.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Four
An electric dipole is a pair of equal and opposite charges \( q \) and \( -q \) placed a distance \( 2a \) apart. Its dipole moment has magnitude \( p=q\times2a \).
The statements that are correct:
(A) Total charge of the dipole is zero — correct
(C) Far field falls off as \( 1/r^{3} \) — correct
(E) No net force in a uniform field — correct
(G) No torque when \( \vec p \) is along \( \vec E \) — correct
The statements that are not:
(B) Direction of the dipole — it is taken from \( -q \) to \( +q \).
(D) Same field in all directions — the dipole field depends on the angle between \( \vec r \) and \( \vec p \) too.
(F) Dipole moment of \( \mathrm{CO_2} \) — its centres of positive and negative charge lie at the same place, so it has no permanent dipole moment.
Number of correct statements = 4
NCERT (2026-27):
Electric Dipole – “An electric dipole is a pair of equal and opposite point charges q and –q, separated by a distance 2a. The line connecting the two charges defines a direction in space. By convention, the direction from –q to q is said to be the direction of the dipole. …”
Electric Dipole – “The total charge of the electric dipole is obviously zero. This does not mean that the field of the electric dipole is zero. …”
The field of an electric dipole – “Notice the important point that the dipole field at large distances falls off not as 1/r2 but as 1/r3. Further, the magnitude and the direction of the dipole field depends not only on the distance r but also on the angle between the position vector r and the dipole moment p.”
Dipole in a Uniform External Field – “There is a force qE on q and a force –qE on –q. The net force on the dipole is zero, since E is uniform. …”
Dipole in a Uniform External Field – “This torque will tend to align the dipole with the field E. When p is aligned with E, the torque is zero.”
Physical significance of dipoles – “In most molecules, the centres of positive charges and of negative charges lie at the same place. Therefore, their dipole moment is zero. CO2 and CH4 are of this type of molecules. …”