Magnetism and Matter
Magnetic phenomena are found everywhere from distant galaxies to tiny atoms and even within the Earth itself, which acts like a giant magnet. A freely suspended bar magnet always points north-south, with like poles repelling and unlike poles attracting each other. Unlike electric charges, magnetic poles cannot exist alone breaking a magnet gives smaller magnets with both poles. Magnets can also be made from iron and its alloys. In this chapter we study bar magnets, Gauss’s law of magnetism, and types of magnetic materials like paramagnetic, diamagnetic and ferromagnetic.
Magnetism and Matter Class 12th Topics(NCERT Syllabus)
1. Introduction
Magnetic phenomena are found everywhere from distant galaxies to tiny atoms and even within the Earth itself, which acts like a giant magnet. A freely suspended bar magnet always points north-south, with like poles repelling and unlike poles attracting each other. Unlike electric charges, magnetic poles cannot exist alone breaking a magnet gives smaller magnets with both poles. Magnets can also be made from iron and its alloys. In this chapter we study bar magnets, Gauss’s law of magnetism, and types of magnetic materials like paramagnetic, diamagnetic and ferromagnetic.
2. Bar Magnet
A bar magnet has two poles north and south. It always aligns in the north-south direction when suspended freely. Like poles repel, unlike poles attract, and magnetic field lines go from the north pole to the south pole.
- Bar Magnet
- Magnetic Field Lines
- Bar magnet as an equivalent solenoid
- The dipole in a uniform magnetic field
3. Magnetism and Gauss’s Law
Gauss's law for magnetism states that the net magnetic flux through any closed surface is always zero.
$$
\oint \vec{B} \cdot d \vec{A}=0
$$
This means magnetic field lines are continuous loops - they never start or end, unlike electric charges.
4. Magnetisation and Magnetic Intensity
- Magnetisation (M):
It is the magnetic moment per unit volume of a material.$$M=\frac{\text { Magnetic moment }}{\text { Volume }}$$
It tells how strongly a material is magnetised. - Magnetic Intensity (H):
It is the external magnetic field applied to magnetise a material.
$$B=\mu_0(H+M)$$
Here, $B$ is the magnetic field, $H$ is magnetic intensity, and $M$ is magnetisation.
5. Magnetic Properties of Materials
- Diamagnetic materials – Weakly repelled by a magnetic field (e.g., copper, bismuth).
- Paramagnetic materials – Weakly attracted to a magnetic field (e.g., aluminium, platinum).
- Ferromagnetic materials – Strongly attracted and can be permanently magnetised (e.g., iron, cobalt, nickel).
Exam-wise Weightage of Magnetism and Matter
| Exam | Approximate Weightage | Remarks |
|---|---|---|
| NEET | 1-2 Questions | Mostly conceptual questions and simple numericals; magnets, magnetic materials. |
| Board | 5 marks | Theory (magnetic properties, Gauss’s law), derivations, some numerical problems. |
| JEE | 1-2 Questions | Includes tricky numericals (magnetic field, coil torque), conceptual depth required. |
Approach to Solve Magnetism and Matter Questions
To answer problems of class 12th Physics Magnetism and Matter, first of all, read Question carefully and find out if it's a conceptual or numerical one. Remember the key concept: a bar magnet can be treated as a magnetic dipole, and by Gauss's law of magnetism, the total magnetic flux passing through a closed surface is always zero. Keep in mind the nature of materials diamagnetic materials exhibit weak negative susceptibility, paramagnetic materials exhibit small positive susceptibility and ferromagnetic materials exhibit very high positive susceptibility and create strong magnets. For numerical problems, apply simple formulas such as magnetic moment, torque on a dipole, or relationship between B, H, and M. For theory questions, write in concise points and also provide neat diagrams wherever possible, like field lines of a bar magnet or earth's magnetic field. In this way, you can get full marks in board exams as well as in competitive exams.
Magnetism and Matter: Real-Life Examples
- Compass needle – It always aligns along the Earth’s magnetic field and helps in navigation.
- Refrigerator magnets – Small bar magnets used to stick notes or pictures on fridge doors.
- Earth’s magnetism – Protects us from harmful cosmic rays by deflecting charged particles from the sun.
- Magnetic materials in industries – Iron, cobalt, and nickel are used to make permanent magnets for motors and generators.
- MRI machines – Strong magnetic fields are used in hospitals to take detailed images of the human body.
Related Topics,
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Importance of Magnetism and Matter Class 12
A significant chapter in Physics deals with magnetism and matter. When the matter is subjected to magnetism, it responds in a certain way. The production of a variety of magnetic materials is triggered by the presence of a magnetic field. Magnetism And Matter Class 12 goes into much detail on every topic related to magnets. The chapter on magnetism and matter is crucial for CBSE students' exams. The fundamental principles covered in this chapter serve as a foundation for more advanced subjects. It is critical that these notions are understood from the start. Not only for the CBSE students class 12 physics ch 5 magnetism and matter is important but it also has a heavy weightage in NEET and JEE. it becomes an important chapter because it has a lot of theory about which direct questions are asked so it becomes an easy score topic
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Frequently Asked Questions (FAQs)
The most paramagnetic substance is manganese (Mn).
Refrigerator and freezer doors are sealed with magnets to provide a secure seal. They provide electricity to stereo speakers, earphones, and TVs. Magnets are used to store data in computers and are crucial in scanning devices known as MRIs (magnetic resonance imagers), which doctors use to examine people's inside organs.
Hard magnetic materials or hard ferromagnets are ferromagnetic materials that hold their magnetism for an extended length of time. Alnico (an alloy of iron, aluminium, nickel, cobalt, and copper) and naturally occurring lodestone are two hard magnetic minerals. Material for permanent magnets should have a high retentivity and coercivity. Soft magnetic materials or soft ferromagnets are ferromagnetic materials that keep their magnetism as long as the external field exists. Soft ferromagnets are made out of soft iron. Electromagnets are made from this type of material.
Magnetism accounts for around 2% of the total number of questions presented in the previous eight years, according to the NEET Chapter Wise Weightage for the NEET medical entrance test.
The magnetic field inside the paramagnetism material (B) is larger than the magnetic field in empty space
Paramagnetism material has a relative permeability larger than one.
Paramagnetic substances have a low and positive magnetic susceptibility.
Around two questions regarding magnetism are asked in the jee main test, accounting for around 6.6 per cent of the whole exam.