Class 12 Physics NCERT Solutions: Magnetism and Matter Important Questions

Physics is a fundamental subject for Class 12 students, especially for those aspiring to pursue engineering, pure sciences, or medical fields. One of the critical chapters in the Class 12 Physics curriculum is "Magnetism and Matter." This chapter forms the foundation of various advanced concepts in electromagnetism, electronics, and quantum mechanics. The chapter not only covers the basic properties and laws of magnetism but also dives deep into its applications and real-world phenomena.

This article will cover important questions from the "Magnetism and Matter" chapter of the Class 12 NCERT Physics textbook. It will provide a comprehensive overview of the chapter and equip you with key concepts, formulas, and answers to some frequently asked questions. Let's get started!

Overview of the Chapter: Magnetism and Matter

"Magnetism and Matter" is Chapter 5 of the Class 12 NCERT Physics textbook. This chapter focuses on:

Magnetic Field and Magnetic Dipole:
- Magnetic dipoles and magnetic dipole moments.
- The behavior of magnetic dipoles in uniform and non-uniform magnetic fields.
- Bar magnets as equivalent to a current loop.
- Magnetic field lines and their properties.
Magnetic Properties of Materials:
- Different types of magnetic materials: Diamagnetic, Paramagnetic, and Ferromagnetic.
- Magnetic susceptibility and permeability.
- Curie’s Law.
- Hysteresis loop and its significance.
Earth's Magnetism:
- Magnetic elements of Earth: Magnetic declination, inclination, and horizontal component.
- Magnetic field variations and their causes.
- Dynamo theory and the Earth's magnetic field.
Magnetization and Magnetic Intensity:
- Concepts of magnetization (M) and magnetic intensity (H).
- Relation between M, H, and the magnetic field (B).

These topics are crucial not only for board exams but also for competitive exams like JEE, NEET, and others.

Important Questions from "Magnetism and Matter"

Below is a list of important questions based on the NCERT Class 12 Physics chapter "Magnetism and Matter." These questions are divided into different sections, including short-answer questions, long-answer questions, and numerical problems.

Section A: Short-Answer Questions

What is a magnetic dipole? How is a bar magnet considered a magnetic dipole?
- A magnetic dipole is a system that has two equal and opposite magnetic poles separated by a small distance. A bar magnet is considered a magnetic dipole because it has two poles—north and south—at its ends. The magnetic field of a bar magnet resembles the field generated by a current-carrying loop, making it analogous to a dipole.
Define magnetic declination and inclination.
- Magnetic Declination is the angle between the magnetic meridian (direction of Earth's magnetic field) and the geographic meridian (true north direction) at a given location.
- Magnetic Inclination (or Dip) is the angle that the Earth's magnetic field makes with the horizontal plane at a given point on the Earth's surface.
Explain Curie’s Law in brief.
- Curie’s Law states that the magnetization of a paramagnetic material is directly proportional to the applied magnetic field and inversely proportional to the absolute temperature of the material. Mathematically, $M = \frac{C \times B}{T}$ , where $M$ is magnetization, $B$ is the magnetic field, $T$ is the temperature, and $C$ is the Curie constant.
What is the difference between Diamagnetic, Paramagnetic, and Ferromagnetic materials?
- Diamagnetic materials: Weakly repelled by a magnetic field, have negative susceptibility.
- Paramagnetic materials: Weakly attracted by a magnetic field, have positive susceptibility, and magnetization is proportional to the applied field.
- Ferromagnetic materials: Strongly attracted by a magnetic field, exhibit spontaneous magnetization, and have a positive and very high susceptibility.
Explain the concept of magnetic susceptibility and its significance.
- Magnetic Susceptibility (χ) is a measure of how much a material will become magnetized in an applied magnetic field. It is defined as $χ = \frac{M}{H}$ , where $M$ is magnetization and $H$ is the magnetic field intensity. It helps in classifying materials into diamagnetic, paramagnetic, and ferromagnetic categories.
Describe the hysteresis loop. What does it signify about a material?
- A hysteresis loop shows the relationship between magnetic field strength (H) and magnetization (B) for a ferromagnetic material. The loop signifies how the material retains magnetization even after the external magnetic field is removed. It provides insight into properties like coercivity, retentivity, and magnetic saturation.

Section B: Long-Answer Questions

Describe the elements of Earth’s magnetic field and their significance in navigation.
- The Earth’s magnetic field consists of three elements: Magnetic Declination (D), Magnetic Inclination (I), and Horizontal Component (H). These elements help in navigation as they determine the true geographic direction.
- Declination is the deviation of the compass needle from true north.
- Inclination indicates the angle of Earth's magnetic field with the horizontal.
- Horizontal Component helps in measuring the strength of the magnetic field in the horizontal direction.
Discuss the domain theory of ferromagnetism. How does it explain the magnetic properties of ferromagnetic materials?
- The Domain Theory of Ferromagnetism suggests that a ferromagnetic material consists of small regions called domains, where magnetic moments are aligned in the same direction. In the absence of an external field, these domains are randomly oriented, resulting in no net magnetization. When an external field is applied, domains align in the direction of the field, causing the material to become strongly magnetized.
- This theory explains phenomena such as hysteresis, coercivity, and saturation magnetization in ferromagnetic materials.
Explain the working of a magnetic compass and how the Earth’s magnetic field affects its operation.
- A magnetic compass works on the principle that a freely suspended magnet aligns itself with the Earth’s magnetic field. The needle of the compass, which is magnetized, points towards the magnetic north and south poles of the Earth. Due to magnetic declination, the needle does not point exactly to the true north. Compass readings must be corrected based on the local magnetic declination to find the true direction.
What is the significance of the hysteresis loop in selecting materials for making permanent magnets and electromagnets?
- The hysteresis loop of a material provides important information about its magnetic properties:
- For permanent magnets, materials with a wide hysteresis loop, high coercivity, and high retentivity are chosen to ensure the magnet retains its magnetization.
- For electromagnets, materials with a narrow hysteresis loop, low coercivity, and high permeability are preferred to minimize energy loss and achieve quick magnetization and demagnetization.
Describe how the Earth’s magnetic field is generated and mention some phenomena associated with it.
- The Earth’s magnetic field is generated by the movement of molten iron and nickel in the Earth's outer core. This movement, combined with the rotation of the Earth, creates electric currents that generate a magnetic field, a process explained by the Dynamo Theory.
- Phenomena associated with Earth’s magnetic field include magnetic storms, auroras (Northern and Southern Lights), and the wandering of magnetic poles.

Section C: Numerical Problems

Calculate the magnetic field at a point on the axial line of a bar magnet of length 10 cm, having a magnetic moment of 1.5 A-m², at a distance of 20 cm from its center.
Given:
- Magnetic moment, $M = 1.5 \, A-m^2$
- Distance, $d = 20 \, cm = 0.2 \, m$
- Length of the magnet, $l = 10 \, cm = 0.1 \, m$
Magnetic field on the axial line of a bar magnet is given by:
$B = \frac{{\mu_0}}{{4\pi}} \frac{{2Md}}{{(d^2 - l^2)^2}}$
After substituting the values and solving, you get the answer.
A magnet of magnetic moment 0.5 A-m² is freely suspended in a uniform magnetic field of strength 0.1 T. Calculate the torque acting on the magnet if it is inclined at 30° to the direction of the magnetic field.
Given:
- Magnetic moment, $M = 0.5 \, A-m^2$
- Magnetic field strength, $B = 0.1 \, T$
- Angle, $\theta = 30°$
Torque is given by:
$\tau = MB \sin\theta$
Substituting the values, we get:
$\tau = 0.5 \times 0.1 \times \sin 30° = 0.025 \, Nm$
A circular coil of 200 turns and radius 10 cm carries a current of 5 A. Calculate the magnetic field at a point along its axis at a distance of 20 cm from the center of the coil.
Given:
- Number of turns, $n = 200$
- Radius, $r = 10 \, cm = 0.1 \, m$
- Current, $I = 5 \, A$
- Distance, $x = 20 \, cm = 0.2 \, m$
Magnetic field on the axis of a circular current loop is given by:
$B = \frac{{\mu_0 n I r^2}}{{2 (r^2 + x^2)^{3/2}}}$
Substituting the values and solving will provide the result.

Conclusion

The "Magnetism and Matter" chapter in Class 12 Physics is crucial for understanding various fundamental concepts of magnetism and its real-life applications. This chapter not only lays the foundation for higher studies in physics and engineering but also helps students appreciate the natural phenomena around us, such as Earth's magnetism. By mastering the important questions and solving related numerical problems, students can solidify their understanding of the subject and perform exceptionally well in their exams.

If you're preparing for competitive exams, remember to focus on understanding the concepts rather than just memorizing them. Practice the numerical problems regularly and stay updated with the latest NCERT solutions and question patterns to ensure comprehensive preparation.