Chapter summary — Magnetism and Matter
This chapter classifies materials by their magnetic behaviour: diamagnetic (weakly repelled; χ<0), paramagnetic (weakly attracted; χ>0), ferromagnetic (strongly attracted; spontaneous magnetisation), antiferromagnetic and ferrimagnetic. Important concepts include magnetisation M, magnetic susceptibility χ and permeability μ (μ = μ0(1+χ)), hysteresis loop, retentivity and coercivity, Curie temperature (Tc), domain theory for ferromagnetism, applications like transformers and permanent magnets, and the distinction between B (magnetic flux density) and H (magnetic field intensity). Key formulas: M = χH, B = μ0(H+M) = μH, torque on magnetic dipole τ = μ × B.
Revision tips: Memorize signs of χ for dia/para/ferro, relationships between B,H,M, and basic features of hysteresis (area = energy loss). Practice numeric problems on susceptibility, relative permeability and behavior across Curie temperature.
1. Diamagnetic materials are characterised by:
A) Strong attraction to magnetic field
B) Weak repulsion (χ < 0) ✅
C) Permanent magnetisation
D) High coercivity
2. Which of the following materials is paramagnetic?
A) Copper
B) Aluminium ✅
C) Iron (ferromagnetic)
D) Bismuth (diamagnetic)
3. Ferromagnetic materials exhibit:
A) Spontaneous magnetisation and domain formation ✅
B) Weak repulsion
C) No magnetic response
D) Linear M-H relation only
4. Magnetic susceptibility χ is defined as:
A) M/B
B) M/H ✅
C) B/H
D) H/M
5. The relation between B, H and M in SI units is:
A) B = μ0 H
B) B = μ0(H + M) ✅
C) B = M/H
D) B = H/μ0
6. Relative permeability μ_r is given by:
A) μ/μ0 ✅
B) μ0/μ
C) μ0·μ
D) μ−μ0
7. For paramagnetic materials, the susceptibility:
A) Is negative
B) Is positive and small ✅
C) Is very large and positive
D) Is zero
8. Curie temperature (Tc) is the temperature above which:
A) Paramagnet becomes diamagnet
B) Ferromagnet loses spontaneous magnetisation (becomes paramagnetic) ✅
C) Diamagnet becomes ferromagnet
D) Magnetic susceptibility becomes infinite
9. Hysteresis loop area represents:
A) Energy loss per cycle (hysteresis loss) ✅
B) Magnetic moment
C) Maximum magnetisation
D) Coercivity only
10. Retentivity (remanence) is the value of:
A) Coercive field
B) Remaining flux density when H=0 after saturation ✅
C) Initial magnetisation
D) Magnetic susceptibility
11. Coercivity is defined as:
A) Field required to saturate magnet
B) Field required to reduce magnetisation to zero after saturation ✅
C) Magnetic moment per unit volume
D) Magnetic flux density
12. Which material is commonly used for permanent magnets due to high coercivity?
A) Soft iron
B) Steel alloys (e.g., Alnico) ✅
C) Pure iron
D) Copper
13. Soft magnetic materials have:
A) High coercivity and high hysteresis loss
B) Low coercivity and low hysteresis loss ✅
C) No magnetisation
D) Negative susceptibility
14. Magnetic domains are:
A) Small regions with uniform magnetisation inside ferromagnets ✅
B) Regions of zero magnetisation only
C) Only in paramagnets
D) Regions of charge
15. The SI unit of magnetic susceptibility (volume susceptibility) is:
A) SI unitless (dimensionless) ✅
B) A·m^2
C) Tesla
D) Weber
16. Diamagnetism arises due to:
A) Unpaired electrons
B) Change in orbital motion of electrons producing induced magnetic moments opposite to applied field ✅
C) Exchange interaction
D) Permanent magnetic moments aligned
17. Langevin's theory explains magnetism in:
A) Ferromagnetism
B) Paramagnetism and diamagnetism (classical) ✅
C) Superconductivity
D) Ferrimagnetism
18. Magnetic field intensity H has SI unit:
A) A/m ✅
B) Tesla
C) Weber
D) Ohm
19. Magnetic flux density B has SI unit:
A) Tesla (T) ✅
B) A/m
C) Weber/m
D) Henry
20. Relative permeability μ_r for vacuum is:
A) 0
B) 1 ✅
C) >1 always
D) <0
21. Ferrimagnetic materials differ from ferromagnetic in that:
A) Magnetic moments of sublattices are unequal and antiparallel ✅
B) They are diamagnetic
C) They have no domains
D) They are non-magnetic
22. Antiferromagnetic materials have:
A) Net zero magnetisation due to equal antiparallel moments ✅
B) Strong net magnetisation
C) Diamagnetic behaviour
D) High coercivity
23. Magnetisation M is defined as magnetic moment per unit:
A) Volume ✅
B) Mass
C) Length
D) Area
24. Relative permeability μ_r is related to susceptibility by:
A) μ_r = 1 + χ ✅
B) μ_r = χ − 1
C) μ_r = χ/μ0
D) μ_r = μ0χ
25. Magnetic hysteresis is most important in deciding:
A) Core losses in transformers and design of permanent magnets ✅
B) Electrical conductivity
C) Optical properties
D) Thermal conductivity
26. Which of these materials shows high magnetic permeability and is used as transformer core?
A) Hard steel
B) Soft iron (or silicon steel) ✅
C) Copper
D) Glass
27. Magnetic coercivity of a material indicates its ability to:
A) Retain magnetisation (resistance to demagnetisation) ✅
B) Conduct electricity
C) Expand on magnetisation
D) Emit electrons
28. Curie point of iron is approximately:
A) 100 °C
B) 770 °C (approx) ✅
C) 0 °C
D) 2000 °C
29. In a hysteresis loop, saturation magnetisation means:
A) Maximum magnetisation under very high H when all domains aligned ✅
B) Zero magnetisation
C) Minimum energy state
D) Negative magnetisation
30. The process of making a material magnetic by applying magnetic field is called:
A) Magnetisation ✅
B) Demagnetisation
C) Polarisation
D) Ionization
31. Which of following has negative susceptibility?
A) Diamagnetic materials (e.g., Bismuth) ✅
B) Paramagnetic materials
C) Ferromagnetic materials
D) Ferrimagnetic
32. The net magnetic moment in a ferrimagnet is due to:
A) Unequal antiparallel magnetic moments of sublattices ✅
B) Equal antiparallel moments
C) No moments
D) Thermal agitation only
33. Magnetostriction refers to:
A) Change in dimensions of a ferromagnet when magnetised ✅
B) Change in electrical resistance under magnetisation
C) Emission of electrons
D) None
34. A material with very high coercivity and remanence is known as:
A) Hard magnetic material (used for permanent magnets) ✅
B) Soft magnetic material
C) Diamagnet
D) Superconductor
35. Which of the following techniques measures magnetic susceptibility?
A) Gouy balance / Faraday balance ✅
B) Spectrophotometry
C) Calorimetry
D) Potentiometry
36. Exchange interaction is responsible for:
A) Ferromagnetism and antiferromagnetism (quantum origin) ✅
B) Diamagnetism only
C) Paramagnetism classical only
D) Superconductivity
37. London's theory is associated with:
A) Superconductivity (London equations) ✅
B) Diamagnetism
C) Paramagnetism
D) None
38. The magnetic field inside a long solenoid filled with material of permeability μ is approximately:
A) B = μ n I ✅
B) B = μ0 n I
C) B = n I / μ
D) B = 0
39. Which material shows zero resistance and perfect diamagnetism below critical temperature?
A) Superconductor (Meissner effect) ✅
B) Ferromagnet
C) Paramagnet
D) Ferrimagnet
40. The magnetisation curve (M vs H) for ferromagnet shows:
A) Non-linear behaviour and saturation ✅
B) Linear and no saturation
C) Negative slope only
D) Zero magnetisation
41. Magnetic circuits are analogous to electric circuits where magnetic reluctance is analogous to:
A) Resistance ✅
B) Capacitance
C) Inductance
D) Conductance
42. The SI unit of magnetic moment is:
A) A·m^2 ✅
B) Tesla
C) Weber
D) Ampere
43. Ferromagnetic resonance involves:
A) Resonant precession of magnetisation in a magnetic field ✅
B) Thermal resonance
C) Optical resonance
D) Electrical resonance
44. Paramagnetic susceptibility follows Curie's law: χ = C/T, meaning susceptibility:
A) Decreases with increasing temperature ✅
B) Increases with temperature
C) Independent of temperature
D) Negative
45. Which of these is a ferrimagnetic material commonly used in ceramic magnets?
A) Magnetite (Fe3O4) ✅
B) Copper
C) Gold
D) Silicon
46. When a ferromagnetic specimen is heated above Curie temperature and cooled in absence of field, it:
A) Returns to paramagnetic state with no remanence ✅
B) Becomes permanently magnetised
C) Becomes diamagnetic
D) Converts to superconductor
47. The phenomenon in which magnetic domains align to produce a net magnetisation on applying field is called:
A) Domain rotation and domain wall motion (magnetisation) ✅
B) Electrification
C) Polarisation only
D) Ionisation
48. Magnetic after-effect or magnetic viscosity refers to:
A) Time-dependent change in magnetisation after application/removal of field ✅
B) Viscosity change under field
C) Electrical resistance change
D) Instantaneous change only
49. Which of the following statements is TRUE?
A) χ(ferromagnet) >> χ(paramagnet) >> |χ(diamagnet)| ✅
B) χ(diamagnet) > χ(paramagnet)
C) χ values are negative for paramagnets
D) χ is same for all materials
50. The primary reason ferromagnetism disappears above Curie temperature is:
A) Thermal agitation overcomes exchange interaction aligning moments ✅
B) Electrons disappear
C) Magnetic field vanishes
D) Permeability becomes infinite