Magnetism and Matter

part 1

Bar Magnet and Earth's Magnetism

• Bar magnet as equivalent solenoid
• Magnetic field lines of a bar magnet
• Earth's magnetic field and magnetic elements
• Apparent and true dip

part 2

Magnetic Properties of Materials

• Magnetisation and magnetic intensity
• Magnetic susceptibility and permeability
• Dia, para and ferromagnetic substances

part 3

Permanent Magnets and Electromagnets

• Hysteresis loop and B-H curve
• Permanent magnets and electromagnets
• Applications of magnetic materials

Bar magnet: B on axial point

$B = \frac{\mu_0}{4\pi} \cdot \frac{2M}{r^3}$

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Bar magnet: B on equatorial point

$B = \frac{\mu_0}{4\pi} \cdot \frac{M}{r^3}$

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Torque on bar magnet in field

$\tau = MB\sin\theta = \vec{M}\times\vec{B}$

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Curie's law (paramagnetism)

$M = \frac{CB}{T}$ (C = Curie constant)

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Earth's magnetic field components

$B_v = B\sin\delta$; $B_H = B\cos\delta$

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Distinguish between diamagnetic, paramagnetic and ferromagnetic materials on the basis of (i) susceptibility, (ii) behaviour in a non-uniform magnetic field, and (iii) effect of temperature.

The susceptibility of a magnetic material is −0.085. Identify the type of magnetic material and state its behaviour in an external magnetic field.

State Curie's law for a paramagnetic material. How does the magnetic susceptibility of a paramagnetic substance vary with absolute temperature?

Define the terms (i) magnetic declination and (ii) angle of dip at a place. At what places on the earth's surface is the angle of dip 90°?

Derive an expression for the magnetic field on the axial line of a magnetic dipole (bar magnet) at a distance r from its centre, for r much greater than the length of the magnet.

Why is soft iron preferred over steel for making the core of an electromagnet?

A bar magnet of magnetic moment m is placed in a uniform magnetic field B. Derive an expression for the torque acting on it and hence for the potential energy stored in the magnet for its different orientations in the field.

Define the terms magnetic intensity (H), intensity of magnetisation (M) and magnetic susceptibility. Write the relation connecting them with relative permeability.

At a place on the earth, the angle of dip is 0°. What can you conclude about the location of that place?

How many marks is Magnetism and Matter worth in the Class 12 board exam?

Around 5 marks of the 70-mark CBSE Physics theory paper, based on the official unit-wise weightage. Focus on dia/para/ferromagnetism comparison table.

Is Magnetism and Matter easy or hard?

It's rated medium — a moderate-difficulty chapter in Class 12 Physics. Most students need about 3 hours to cover it well.

What are the important topics in Magnetism and Matter?

The chapter covers 10 NCERT topics in 3 areas: Bar Magnet and Earth's Magnetism; Magnetic Properties of Materials; Permanent Magnets and Electromagnets.

What questions come from Magnetism and Matter in board exams?

Between 2018–2024, CBSE board papers asked questions from this chapter on Magnetic Materials, Magnetic Susceptibility, Curie's Law, Earth's Magnetism — 1- to 3-mark questions.