Match List-I with List-II.
| List-I | List-II |
|---|---|
| (A) Dipole in a uniform field, with \(\vec p\) at an angle \(\theta\) to \(\vec E\) | (I) Net force in the direction of increasing field |
| (B) Dipole in a non-uniform field, with \(\vec p\) parallel to \(\vec E\) | (II) No torque and no net force |
| (C) Dipole in a non-uniform field, with \(\vec p\) antiparallel to \(\vec E\) | (III) Torque \(pE\sin\theta\) and no net force |
| (D) Dipole in a uniform field, with \(\vec p\) parallel to \(\vec E\) | (IV) Net force in the direction of decreasing field |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A)-(III), (B)-(I), (C)-(IV), (D)-(II)
(A) Dipole in a uniform field, with \( \vec p \) at an angle \( \theta \) to \( \vec E \) — This matches (III). The forces \( q\vec E \) and \( -q\vec E \) are equal and opposite, so the net force is zero. They act at different points and form a couple of torque \( pE\sin\theta \).
(B) Dipole in a non-uniform field, with \( \vec p \) parallel to \( \vec E \) — This matches (I). The charge \( q \) sits where the field is stronger, so the force on it is larger than the force on \( -q \). The net force points towards the stronger field.
(C) Dipole in a non-uniform field, with \( \vec p \) antiparallel to \( \vec E \) — This matches (IV). Now the charge \( -q \) sits in the stronger field, and the net force points towards the weaker field.
(D) Dipole in a uniform field, with \( \vec p \) parallel to \( \vec E \) — This matches (II). With \( \theta=0 \) the torque \( pE\sin\theta \) is zero, and a uniform field gives no net force.
NCERT (2026-27):
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 – “… The magnitude of p × E is also p E sinθ and its direction is normal to the paper, coming out of it.”
Dipole in a Uniform External Field – “It is easily seen that when p is parallel to E, the dipole has a net force in the direction of increasing field. When p is antiparallel to E, the net force on the dipole is in the direction of decreasing field.”
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.”