# Magnetism and Matter Notes, Class 12 Physics | SwaVid

Magnetism and Matter, NCERT Class 12 Physics: notes with key ideas, formulas, common mistakes and 3 quick checks with worked answers.

Canonical: https://www.swavid.com/cbse/class-12/physics/chapter/magnetism-and-matter

Source: https://www.swavid.com/cbse/class-12/physics/chapter/magnetism-and-matter

# Magnetism and Matter

## Formulas and definitions

## Key ideas

## Common mistakes

## Quick checks

## Keep going

## Questions parents ask

## Class 12 Physics on SwaVid

### Bar magnet as a dipole

### Magnetic field lines

### Gauss's law for magnetism

### Magnetisation and magnetic intensity

### Classification of magnetic materials

### Next chapter

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SwaVid › CBSE › Class 12 › Physics › Magnetism and Matter

Notes written by SwaVid from the NCERT textbook.

Class 12 Physics, Chapter 5. Key ideas, formulas and common mistakes.

CBSE prints 17 marks for Units III-IV together, not for this chapter alone.

Short answer. This chapter examines the magnetic properties of bar magnets, magnetic dipole moments, and Gauss's law for magnetism. It explains how magnetic field lines behave and classifies magnetic materials into diamagnetic, paramagnetic, and ferromagnetic substances.

Source: NCERT Physics Part I (Reprint 2026-27) , Chapter 5, Magnetism and Matter

A bar magnet acts as a magnetic dipole with a magnetic moment directed from its south pole to its north pole. Its magnetic field patterns resemble those of a finite current-carrying solenoid.

Magnetic field lines form continuous closed loops without beginning or ending. The tangent to a field line at any point gives the direction of the magnetic field at that point, and lines never intersect.

The net magnetic flux through any closed surface is always zero. This law establishes that isolated magnetic poles or monopoles do not exist in nature.

Magnetisation M is the net magnetic dipole moment per unit volume of a material. Magnetic intensity H represents the external magnetising field, related by B = μ₀ (H + M).

Materials are grouped into diamagnetic, paramagnetic, and ferromagnetic based on their response to an external field. Diamagnets are weakly repelled, paramagnets are weakly attracted, and ferromagnets are strongly attracted.

Try each question first. Then tap it to see the answer.

B axial = (μ₀ / 4π) × (2m / r³)

B axial = 10⁻⁷ × (2 × 0.5) / (0.1)³

B axial = 10⁻⁷ × 1 / 10⁻³ = 10⁻⁴ T

10⁻⁴ T

τ = m B sin θ

τ = 0.40 × 0.20 × sin 30°

τ = 0.08 × 0.5 = 0.04 N m

0.04 N m

μ r = 1 + χ

μ r = 1 + 0.00015 = 1.00015

Since χ is small and positive, the substance is paramagnetic.

μ r = 1.00015, Paramagnetic

Electromagnetic Induction .

Moving Charges and Magnetism .

The 14 chapters of Class 12 Physics .

CBSE does not give marks to one chapter. It prints 17 marks for Units III-IV together (Magnetic Effects of Current and Magnetism; Electromagnetic Induction and Alternating Currents). Magnetism and Matter is part of that group.

No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed.

Electromagnetic Induction.

SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works.

- Ch 5 NCERT book
- 17 marks, Units III-IV together
- 3 quick checks
- Treating magnetic field lines as starting at north poles and ending at south poles . Remember that magnetic field lines form continuous closed loops. They run from north to south outside the magnet, and from south to north inside the magnet.
- Using Gauss's law for magnetism to find a non-zero net flux . Because magnetic monopoles do not exist, every field line that enters a closed surface must also exit it. The total magnetic flux across any closed surface is strictly zero.
- Confusing magnetic intensity H with magnetic field B . H is the external magnetising field measured in A m⁻¹, while B is the total magnetic flux density inside the material measured in tesla. They are related by B = μ₀ (H + M).

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