Match List-I with List-II. List-II gives the typical value of each quantity in List-I.
| List-I | List-II |
|---|---|
| (A) Number of atoms in one domain of a ferromagnetic material | (I) More than 1000 |
| (B) Size of one domain of a ferromagnetic material, in mm | (II) About \(10^{-5}\) |
| (C) Relative magnetic permeability of a ferromagnetic element such as iron | (III) About \(10^{11}\) |
| (D) Fraction by which a diamagnetic bar reduces the field inside it, in most cases | (IV) About 1 |
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)-(I), (D)-(II)
In a ferromagnetic material, the atomic magnetic moments line up on their own over small regions called domains. The size of a domain and the number of atoms in it are fixed typical values. A diamagnetic bar behaves very differently: it weakens the field inside it only slightly.
(A) Number of atoms in one domain of a ferromagnetic material — This matches (III). A typical domain holds about \( 10^{11} \) atoms. All their magnetic moments point in the same direction.
(B) Size of one domain of a ferromagnetic material, in mm — This matches (IV). A typical domain is about 1 mm in size. This is tiny for us, but it is a huge region on the scale of atoms.
(C) Relative magnetic permeability of a ferromagnetic element such as iron — This matches (I). Iron, cobalt, nickel and gadolinium get strongly magnetised in a field. For these elements \( \mu_r \) is more than 1000.
(D) Fraction by which a diamagnetic bar reduces the field inside it, in most cases — This matches (II). A diamagnetic bar pushes the field lines out a little, so the field inside it falls. In most cases the fall is only one part in \( 10^{5} \), that is, about \( 10^{-5} \) of the field.
NCERT (2026-27):
Ferromagnetism – “… Each domain has a net magnetisation. Typical domain size is 1mm and the domain contains about 1011 atoms.”
“… There are a number of elements, which are ferromagnetic: iron, cobalt, nickel, gadolinium, etc. The relative magnetic permeability is >1000!”
Diamagnetism – “… The field lines are repelled or expelled and the field inside the material is reduced. In most cases, this reduction is slight, being one part in 105.”