Magnetism and Matter

Important Topics of Magnetism and Matter

The chapter Magnetism and Matter is devoted to the comprehension of the behaviour of various materials in a magnetic field and the origin of magnetism on a microscopic scale. It describes the magnetism of materials, the behaviour of magnetic dipole and how materials can be classified into magnetic and non-magnetic. The topics can enable the learners to gain a good conceptual knowledge of material magnetism that is vital in Class 12 board exams as well as in competitive exams such as JEE and NEET.

1. Introduction to Magnetism

This topic provides the fundamental idea of magnetism and magnetism. It describes the attraction of some materials by magnets and the distinction between natural magnets and artificial ones. The concept of magnetic poles and the impossibility to separate north and south poles is mentioned. This chapter provides the basis for the study of the magnetic behaviour of matter. It teaches the students to differentiate magnetic effects and other physical phenomena.

2. Bar Magnet and Its Characteristics

This topic studies a bar magnet as a simple and ideal magnetic system. It explains important terms such as magnetic poles, magnetic axis, magnetic length, and magnetic moment. The behaviour of a bar magnet in a magnetic field is discussed. Magnetic field patterns around a bar magnet are introduced using field lines. This topic helps visualise magnetic fields clearly.

3. Magnetic Field and Magnetic Field Lines

This topic explains the concept of a magnetic field as the region around a magnet where magnetic forces act. It introduces magnetic field lines as a way to represent the direction and strength of the magnetic field. The properties of field lines are discussed in detail. This topic helps students understand how magnetic fields are visualised.

4. Magnetic Dipole and Magnetic Dipole Moment.

In this topic, a bar magnet is considered as a magnetic dipole that comprises two identical but opposite poles. It brings in the concept of magnetic dipole moment as a measure of the strength of a magnet. The orientation of the dipole moment is elaborated. This is a fundamental concept in the study of the behaviour of magnets in an external magnetic field. It links magnetism and the theory of dipoles.

5. Magnetisation

The concept presented in this topic is the term magnetization which is the magnetic dipole moment of a substance expressed in unit volume. It describes the response of materials when an external magnetic field is applied to them. Magnetisation assists in the measurement of the magnetism of materials. The concept is necessary in the classification of magnetic materials. It is the foundation of material magnetism.

6. Magnetic Intensity and Magnetic Permeability

In this topic, magnetic field intensity is defined as the magnetic field caused by external sources. The concept of magnetic permeability is added to denote the ease with which a material can be magnetised. The association between magnetic field, magnetization and permeability is addressed. The topic assists in comparing various magnetic materials. It is significant in theory and numericals.

7. Magnetic Susceptibility

This topic brings in magnetic susceptibility as a parameter to measure the response of a substance to a magnetic field. It describes the susceptibility of different materials. The concept aids in categorising materials into diamagnetic, paramagnetic and ferromagnetic. The conceptual significance of this topic is great.

8. Classification of Magnetic Materials

The materials under this topic are classified into diamagnetic, paramagnetic and ferromagnetic materials. It describes the behaviour of each type when subjected to an external magnetic field. Magnetisation, susceptibility and permeability differences are discussed. This topic is significant in the study of material properties. A lot of conceptual examination questions are based on this section.

9. Temperature Dependence of Magnetic Materials

This subject describes the behaviour of the magnetic characteristics of materials at varying temperatures. The law of Curie on paramagnetic substances is covered. The influence of temperature on ferromagnetic material is described. This subject relates magnetism to thermal effects.

10. Permanent Magnets

This topic describes the nature of permanent magnets and the materials employed to produce permanent magnets. Other properties like retentivity and coercivity are mentioned. The variables that influence the power of permanent magnets are described.

Important Formulas of Magnetism and Matter

Significant Formulas of Magnetism and Matter are summaries of the most important mathematical relationships that can be employed to characterise the magnetic properties of materials and magnetic dipoles. These equations are useful in the determination of magnetism, torque, magnetisation, susceptibility, and energy in magnetic systems. These formulae should be revised on a regular basis and used properly to solve numerical and theory-based questions in Class 12 board exams and also in competitive exams such as JEE Main and NEET.

1. Magnetic dipole moment of a bar magnet:

$
\vec{M}=m(2 l)
$

where $m$ is pole strength and $2 l$ is magnetic length.

2. Magnetisation:

$\vec{M}=\frac{\text { Magnetic dipole moment }}{\text { Volume }}$

3. Magnetic Field Intensity and Magnetic Induction:

Relation between magnetic field $\vec{B}$, magnetic intensity $\vec{H}$, and magnetization $\vec{M}$

$
\vec{B}=\mu_0(\vec{H}+\vec{M})
$

4. Magnetic Susceptibility:

$\chi=\frac{M}{H}$

5. Magnetic Permeability:

• Magnetic permeability of a material

$
\mu=\mu_0(1+\chi)
$

• Relative permeability

$
\mu_r=1+\chi
$

6. Classification of Magnetic Materials:

• Diamagnetic materials

$
\chi<0
$

• Paramagnetic materials

$
\chi>0
$

• Ferromagnetic materials

$
\chi \gg 1
$

7. Curie’s Law:

$
\chi=\frac{C}{T}
$

where $C$ is the Curie constant.

Magnetism and Matter: Previous Year Questions

Past Year Questions on Magnetism and Matter assist students in recognising the most widely tested concepts that are concerned with the magnetic nature of materials and magnetic dipoles. Common questions revolving around these are questions of magnetic dipole moment, torque on a magnet, magnetisation, susceptibility and categories of magnetic materials. The practice of PYQs enhances conceptual clarity and helps students learn how theoretical concepts are presented in the exams. This practice is very useful in performing very well in Class 12 board exams, JEE Main and NEET.

Question 1:

An iron rod of susceptibility 599 is subjected to a magnetising field of $1200 \mathrm{~A} \mathrm{~m}^{-1}$. The permeability of the material of the rod is :

$
\left(\mu_o=4 \pi \times 10^{-7} T m A^{-1}\right)
$

Solution:

Given, $\chi_m=599$
Also, $\mu_r=1+\chi_m=600$
We know, $\mu=\mu_r \mu_o$

$
\begin{aligned}
& \mu=600 \times 4 \pi \times 10^{-7} \\
& \mu=2400 \pi \times 10^{-7} \\
& \mu=2.4 \pi \times 10^{-4} T m A^{-1}
\end{aligned}
$

Question 2:

If a magnet of pole strength $m$ is divided into four parts such that the length and width of each part are half that ofthe initial one, then the pole strength of each part will be

Solution:

Pole strength:

$\therefore \quad$ Pole strength for each part $=\mathrm{m}^{\prime}=(\mathrm{m} / 2)$

Question 3:

The distances of two points on the axis of a magnet from its centre are 10 cm and 20 c,m respectively. The ratio of magnetic intensity at these points is $12.5: 1$. The length of the magnet will be:

Solution:

The magnetic field on the axis of a bar magnet of length $2 l$, having a pole strength $m$, at a distance $d$ is

$
\begin{aligned}
& B=\frac{\mu_0}{4 \pi} \frac{m}{[d-l]^2}-\frac{\mu_0}{4 \pi} \frac{m}{[d+l]^2} \\
& B=\frac{\mu_0 m}{4 \pi} \frac{[d+l]^2-[d-l]^2}{\left[d^2-l^2\right]^2}=\frac{\mu_0 m l d}{\pi\left[d^2-l^2\right]^2} \\
& \Rightarrow \frac{B_1}{B_2}=\frac{d_1}{d_2}\left[\frac{d_2^2-l^2}{d_1^2-l^2}\right]^2 \\
& \Rightarrow \frac{12.5}{1}=\frac{10}{20}\left[\frac{400-l^2}{100-l^2}\right]^2 \\
& \Rightarrow l=5 \mathrm{~cm}
\end{aligned}
$
Hence, length of magnet $=2 l=10 \mathrm{~cm}$

Magnetism and Matter in Different Exams

Magnetism and Matter is a relevant theory-based chapter in Class 12 Physics which deals with the magnetic characteristics of substances, and magnetic dipole. The questions in this chapter primarily involve the test of conceptual knowledge, definitions, laws, and material behavior and not long numericals. The exam-wise focus areas and weightage will enable students to focus their attention on board exams and competitive exams such as JEE and NEET.

Important Books and Resources for Class 12 Magnetism and Matter

In order to learn the chapter Magnetism and Matter, the students are advised to consult a set of NCERT textbooks, reference books, and practice books that cover the theory as well as the questions in relation to the applications. It can be used to understand the magnetic properties of materials, magnetic dipoles, magnetization and other related concepts, which are crucial in board examinations or competitive exams such as JEE Main, JEE Advanced and NEET.

Related Topics,

NCERT Resources for Magnetism and Matter

The best learning materials for studying the magnetism characteristics of materials required in the Class 12 Physics syllabus would bethe NCERT resources in Magnetism and Matter. The NCERT textbook and exemplar problems explain concepts such as magnetic dipole, magnetisation, susceptibility, and classification of magnetic materials in a clear and systematic manner. Such resources are crucial to developing good conceptual clarity and preparing efficiently for board examinations and competitive exams such as JEE Main and NEET.

• NCERT solutions for class 12 physics chapter magnetism and matter
• NCERT exemplar solutions for class 12 physics chapter magnetism and matter
• NCERT notes for class 12 physics chapter magnetism and matter

NCERT Subjectwise Resources

NCERT subject-wise materials are organised and syllabus-based learning content on various subjects, which assist students in developing a good conceptual basis. They consist of textbooks, exemplar problems, and solutions and can thus be very helpful in the preparation for the board exams and even competitive exams such as JEE and NEET.

Practice Questions based on Magnetism and Matter

The Magnetism and Matter Practice Questions can be used to support students in their knowledge about the magnetic characteristics of materials and the way of how magnetic dipoles behave. These questions are concerned with magnetic dipole moment, torque on a magnet, magnetisation, susceptibility, the Curie law and classification of magnetic materials. A frequent practice enhances the clarity of concepts, the use of formulas, and the writing of answers. Various problem solving equips the students well to the Class 12 board exam and competitive exams such as JEE Main and NEET.

Conclusion

The chapter Magnetism and Matter contains a solid conceptual foundation upon which materials react to the magnetic field, and magnetism is generated by microscopic magnetic dipoles. Students can reach a good level of conceptual clarity by practising major concepts and important formulas and problem-solving based on the theory of the magnetic dipole moment, magnetisation, susceptibility, and magnetic materials. It is a well-ordered practice that creates confidence and is very successful in passing Class 12 board exams and even in competitive exams such as JEE Main, JEE Advanced and NEET.