Match List-I with List-II.
| List-I | List-II |
|---|---|
| (A) Non-polar molecules in an external field | (I) Net charge appears only on the two faces normal to the field |
| (B) Polar molecules with no external field | (II) Permanent dipoles tend to line up with the field |
| (C) Polar molecules in an external field | (III) Positive and negative charges shift apart, giving an induced dipole |
| (D) A uniformly polarised dielectric slab | (IV) Total dipole moment is zero because of random orientation |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
A dielectric has no free charges. An external field still gives it a net dipole moment, either by stretching non-polar molecules or by turning polar ones.
(A) Non-polar molecules in an external field — This matches (III). The centres of positive and negative charge coincide at first. The field pushes them in opposite directions, and the molecule gets an induced dipole moment.
(B) Polar molecules with no external field — This matches (IV). Each molecule has a permanent dipole, but thermal motion keeps them pointing in random directions. So the total dipole moment is zero.
(C) Polar molecules in an external field — This matches (II). The field turns the permanent dipoles towards its own direction, so a net dipole moment appears along the field.
(D) A uniformly polarised dielectric slab — This matches (I). Inside, the positive end of one dipole sits next to the negative end of the next, so there is no net charge. Unbalanced charge is left only on the two faces normal to the field.
NCERT (2026-27):
Dielectrics and Polarisation – “… The non-polar molecule thus develops an induced dipole moment. …”
Dielectrics and Polarisation – “… In the absence of any external field, the different permanent dipoles are oriented randomly due to thermal agitation; so the total dipole moment is zero. When an external field is applied, the individual dipole moments tend to align with the field. …”
Dielectrics and Polarisation – “… Anywhere inside the dielectric, the volume element Δv has no net charge (though it has net dipole moment). … However, at the surfaces of the dielectric normal to the electric field, there is evidently a net charge density.”