Magnetism is one of the most fascinating topics in Physics. From a small compass needle showing direction to the Earth’s powerful magnetic field protecting life, magnetism plays an important role in our daily life. In Class 12 Physics, the chapter “Magnetism and Matter” explains the magnetic behavior of materials and the origin of magnetism at the atomic level.
This chapter is very important for Board Exams, NEET, and JEE, as it includes theory-based questions, numerical problems, derivations, and conceptual MCQs. In these Magnetism and Matter Class 12 Notes, every topic is explained step by step, in a clear and easy manner, so students can understand concepts deeply and score better marks.
Magnetism and Matter Class 12 Notes PDF | Physics Chapter 5 Full Explanation
1. Magnetic Substances
A magnetic substance is a material that responds to an external magnetic field. When placed near a magnet, some materials get attracted, some are repelled, and some show no noticeable effect.
Based on their behavior, magnetic substances are classified into three main types:
- Diamagnetic substances
- Paramagnetic substances
- Ferromagnetic substances
2. Magnetic Dipole
A magnetic dipole consists of two equal and opposite magnetic poles separated by a small distance. A bar magnet is the best example of a magnetic dipole.
Properties of a Magnetic Dipole:
- It has north and south poles
- Poles always exist in pairs (no isolated magnetic monopole)
- Magnetic field lines emerge from the north pole and enter the south pole
3. Magnetic Dipole Moment
The magnetic dipole moment (M) represents the strength of a magnetic dipole.
Formula:
M = m \times 2l
Where:
- = strength of each pole
- = distance between the poles
SI Unit:
Ampere × meter² (A m²)
The larger the magnetic dipole moment, the stronger the magnet.
4. Bar Magnet as an Equivalent Solenoid
A bar magnet behaves like a current-carrying solenoid. The magnetic field pattern around a bar magnet is similar to that of a solenoid.
Key Similarities:
- Both produce magnetic fields
- Field lines are closed loops
- Both have north and south ends
This concept helps in understanding magnetism from an electrical point of view.
5. Magnetic Field Lines
Magnetic field lines are imaginary lines used to represent magnetic fields.
Characteristics:
- Field lines form closed loops
- Direction is from north to south outside the magnet
- Closer lines indicate stronger magnetic field
- No two magnetic field lines intersect
6. Magnetic Field Due to a Bar Magnet
The magnetic field of a bar magnet can be studied at:
- Axial point
- Equatorial point
(a) Magnetic Field on Axial Line
The axial line passes through the poles of the magnet.
B_{axial} = \frac{\mu_0}{4\pi} \frac{2M}{r^3}
(b) Magnetic Field on Equatorial Line
The equatorial line is perpendicular to the axial line at the center.
B_{equatorial} = \frac{\mu_0}{4\pi} \frac{M}{r^3}
7. Earth’s Magnetism
The Earth behaves like a giant bar magnet, with its magnetic south near the geographic north.
Elements of Earth’s Magnetic Field:
- Magnetic Declination (D)
Angle between geographic and magnetic meridian. - Magnetic Inclination (I)
Angle between Earth’s magnetic field and horizontal plane. - Horizontal Component (H)
Component of Earth’s magnetic field parallel to Earth’s surface.
8. Magnetization
Magnetization (M) is defined as the magnetic moment per unit volume of a material.
M = \frac{\text{Magnetic Moment}}{\text{Volume}}
SI Unit:
A/m
Magnetization explains how strongly a material responds to a magnetic field.
9. Magnetic Intensity (H)
Magnetic intensity represents the external magnetic field applied to a material.
H = \frac{B}{\mu_0} - M
SI Unit:
A/m
10. Magnetic Susceptibility
Magnetic susceptibility () measures how easily a material gets magnetized.
\chi = \frac{M}{H}
Nature of Susceptibility:
- Diamagnetic: Negative and small
- Paramagnetic: Positive and small
- Ferromagnetic: Very large and positive
11. Diamagnetic Substances
Diamagnetic substances are weakly repelled by magnetic fields.
Characteristics:
- Susceptibility is negative
- Independent of temperature
- Magnetization opposite to applied field
Examples:
- Copper
- Gold
- Water
- Bismuth
12. Paramagnetic Substances
Paramagnetic substances are weakly attracted by magnetic fields.
Characteristics:
- Susceptibility is positive
- Decreases with increase in temperature
- Magnetization in the same direction as applied field
Examples:
- Aluminium
- Platinum
- Oxygen
13. Ferromagnetic Substances
Ferromagnetic substances are strongly attracted by magnetic fields.
Characteristics:
- Very large susceptibility
- Can retain magnetism (hysteresis)
- Strong domain alignment
Examples:
- Iron
- Cobalt
- Nickel
14. Curie’s Law
For paramagnetic substances:
\chi = \frac{C}{T}
Where:
- = Curie constant
- = Absolute temperature
This law shows that susceptibility decreases with increase in temperature.
15. Permanent Magnets
Permanent magnets retain magnetism even after the external magnetic field is removed.
Properties:
- High retentivity
- High coercivity
- Used in motors, speakers, compasses
16. Electromagnets
Electromagnets are temporary magnets produced by passing current through a coil.
Advantages:
- Strength can be controlled
- Magnetism disappears when current is off
- Used in cranes, relays, electric bells
17. Comparison: Permanent Magnet vs Electromagnet
| Permanent Magnet | Electromagnet |
|---|---|
| Fixed strength | Adjustable strength |
| Cannot be switched off | Can be switched off |
| Made of steel | Made of soft iron |
18. Important Formulas (Quick Revision)
- Magnetic dipole moment:
- Magnetization:
- Susceptibility:
- Axial field:
- Equatorial field:
19. Exam-Oriented Tips
- Draw neat diagrams in board exams
- Remember differences between dia, para, and ferro
- Practice numericals from susceptibility & magnetic field
- Learn definitions and formulas word by word
Conclusion-Magnetism and Matter Class 12 Notes PDF
The chapter Magnetism and Matter Class 12 builds the foundation for understanding magnetic materials and their real-life applications. With proper understanding of concepts like magnetization, susceptibility, and Earth’s magnetism, students can easily score high marks in exams. These notes are designed to be clear, complete, and exam-ready, making them perfect for revision and concept building.
🔁 Repeated Questions – Magnetism and Matter Class 12 Notes PDF
🔹 1. Very Short Answer Questions (1 Mark)
- What is a magnetic dipole?
- Define magnetic dipole moment. Write its SI unit.
- What is magnetization?
- Define magnetic susceptibility.
- Name any one diamagnetic substance.
- Which material has the highest magnetic susceptibility?
- What is the SI unit of magnetic field intensity?
- Why magnetic monopoles do not exist?
- Write one example of a paramagnetic substance.
- What is the value of susceptibility for vacuum?
🔹 2. Short Answer Questions (2–3 Marks)
- Define magnetization and magnetic intensity. Write their relation.
- What are magnetic field lines? Write any two properties.
- Distinguish between diamagnetic and paramagnetic substances.
- What is magnetic susceptibility? How does it vary with temperature for paramagnetic materials?
- Write any two properties of ferromagnetic substances.
- Explain why a bar magnet is equivalent to a solenoid.
- What is Curie’s law? Write its mathematical expression.
- Define retentivity and coercivity.
- What is Earth’s magnetism?
- Why soft iron is used to make electromagnets?
🔹 3. Short Answer Questions (3–4 Marks)
- Explain the behavior of diamagnetic substances in an external magnetic field.
- Explain paramagnetism on the basis of atomic theory.
- Describe ferromagnetism and explain domain theory.
- What are magnetic field lines? Explain their nature around a bar magnet.
- Write differences between permanent magnet and electromagnet.
- Explain the concept of magnetic dipole moment with diagram.
🔹 4. Long Answer Questions (5 Marks – Board Favorite)
- Derive the expression for the magnetic field at an axial point of a bar magnet.
- Derive the expression for the magnetic field at an equatorial point of a bar magnet.
- Explain Earth’s magnetism. Define magnetic declination, inclination, and horizontal component.
- Classify magnetic materials into diamagnetic, paramagnetic, and ferromagnetic. Compare them on the basis of susceptibility, behavior, and examples.
- Explain the origin of magnetism in materials.
- What is magnetization? Derive the relation between B, H, and M.
🔹 5. Numerical Problems (Repeated)
- A bar magnet has a magnetic dipole moment of ___ A m². Find the magnetic field at a point on its axial line at a distance r.
- Calculate magnetization of a material when magnetic moment and volume are given.
- A material has susceptibility χ = ___. Identify whether it is dia, para, or ferromagnetic.
- Find the ratio of magnetic field at axial and equatorial points of a bar magnet.
- Calculate magnetic intensity when B and M are given.
🔹 6. Assertion–Reason Questions (Common in CBSE)
- Assertion: Diamagnetic substances are repelled by a magnetic field.
Reason: They have no permanent magnetic dipole moment. - Assertion: Ferromagnetic substances show hysteresis.
Reason: They consist of magnetic domains. - Assertion: Paramagnetic susceptibility decreases with temperature.
Reason: Thermal agitation randomizes magnetic moments.
🔹 7. MCQs (Repeated in NEET/JEE)
- Which material is strongly attracted by a magnetic field?
a) Copper
b) Aluminium
c) Iron
d) Water - Magnetic susceptibility of diamagnetic substances is:
a) Positive
b) Zero
c) Negative
d) Infinite - Unit of magnetization is:
a) Tesla
b) Weber
c) A/m
d) A m²
📌 Exam Tip (Important)
👉 Axial & Equatorial field derivations
👉 Differences (Dia, Para, Ferro)
👉 Earth’s magnetism
👉 B = μ₀(H + M)
👉 Curie’s law
We are Completed Magnetism and Matter Class 12 Notes PDF.