Magnetism and Matter Notes for NEET and JEE Main 2027: Key Points, PDF

Magnetism and Matter is Chapter 5 of NCERT Class 12 Physics Part I and part of Unit 13, Magnetic Effects of Current and Magnetism, in both the NEET UG 2026 and JEE Main 2026 syllabi. These notes cover the bar magnet, field lines, a dipole in a uniform field, Gauss’s law for magnetism, magnetisation and dia-, para- and ferromagnetism.

Magnetism and Matter Notes for NEET and JEE Main

Section-wise key points from NCERT Chapter 5, comparison tables, most-asked facts and common mistakes for 2027 revision.

Magnetism and Matter at a Glance

Topics follow the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025 and the JEE Main 2026 syllabus released by the National Testing Agency (NTA); both stay the reference until the 2027 syllabi are out. Full lists: NEET syllabus and JEE Main syllabus.

Bar Magnet and Magnetic Field Lines

Magnets point north-south, like poles repel and unlike poles attract, and cutting a bar magnet only gives two smaller magnets: isolated magnetic poles (monopoles) do not exist.

• Magnetic field lines form continuous closed loops, unlike electric field lines, which start on positive charges and end on negative charges.
• The tangent to a field line gives the direction of B at that point.
• The more field lines cross a unit area, the stronger the field.
• Field lines never intersect, because the field direction at a point must be unique.
• Field lines can be traced by placing a small compass needle at different positions.

Bar Magnet as an Equivalent Solenoid

A bar magnet behaves like a solenoid: both produce similar field patterns, consistent with Ampere’s hypothesis that all magnetism comes from circulating currents.

• Cutting a bar magnet in half is like cutting a solenoid: you get two weaker solenoids, and the field lines stay continuous.
• The far axial field of a finite solenoid is B = (μ₀/4π)(2m/r³), the same as that of a bar magnet of moment m.
• A bar magnet’s magnetic moment equals that of the equivalent solenoid that produces the same field.

Magnetic Dipole in a Uniform Field

A bar magnet in a uniform field feels no net force, only a torque τ = m × B.

• Magnitude of the torque: τ = mB sin θ, where θ is the angle between m and B.
• Potential energy U = −m·B = −mB cos θ, taking U = 0 when m is perpendicular to B.
• U is minimum (−mB) at θ = 0°, the most stable position, and maximum (+mB) at θ = 180°, the most unstable position.
• A compass needle of known moment allowed to oscillate in a field can be used to find either B or m.

Electrostatic Analogue of a Magnetic Dipole

Replacing p by m and 1/ε₀ by μ₀ turns each electric dipole result into the magnetic one.

Gauss’s Law for Magnetism

The net magnetic flux through any closed surface is always zero: Σ B·ΔS = 0.

• This follows from the absence of magnetic monopoles: every field line that enters a closed surface also leaves it.
• Compare Gauss’s law in electrostatics, where the flux equals the enclosed charge divided by ε₀.

Magnetisation and Magnetic Intensity

Magnetisation M is the net magnetic dipole moment per unit volume of a material; the field inside is B = μ₀(H + M).

• M and H have the same unit (A m⁻¹).
• The magnetic flux unit is the weber (1 Wb = 1 T m²), and 1 T = 10⁴ G.

Diamagnetic, Paramagnetic and Ferromagnetic Materials

Materials are classed by their susceptibility: negative for diamagnetic, small and positive for paramagnetic, and large and positive for ferromagnetic.

Key Points on Each Class

• Diamagnetism is present in all substances, but it is weak and is masked in para- and ferromagnetic materials.
• A superconductor is a perfect diamagnet: χ = −1, μᵣ = 0, and the field is completely expelled. This is the Meissner effect, used for example in magnetically levitated trains.
• Ferromagnetic domains are typically about 1 mm across and contain about 10¹¹ atoms. An applied field rotates the domains and makes aligned domains grow.
• Hard ferromagnets keep their magnetisation when the field is removed and make permanent magnets, for example Alnico (iron, aluminium, nickel, cobalt and copper) and naturally occurring lodestone.
• Soft ferromagnets, such as soft iron, lose their magnetisation when the field is removed.

Effect of Temperature on Magnetic Properties

Heat disturbs the alignment of atomic dipoles, so paramagnetic and ferromagnetic magnetisation falls as temperature rises.

• Paramagnetic materials: magnetisation increases as the field is increased or the temperature is lowered, until it saturates when all dipoles are aligned.
• Older NCERT edition (Curie’s law): for a paramagnet, χ = Cμ₀/T, where C is the Curie constant, so susceptibility is inversely proportional to absolute temperature.
• Ferromagnetic materials become paramagnetic at a high enough temperature, as the domain structure breaks up gradually. The older edition calls this transition temperature the Curie temperature T_c, above which χ = C/(T − T_c).

Most-asked Facts for NEET and JEE Main: Magnetism and Matter

Revise these one-line facts from the NCERT chapter just before the exam.

• Magnetic monopoles do not exist; magnetic field lines form closed loops.
• Axial field of a bar magnet is twice its equatorial field at the same distance.
• Torque on a dipole τ = m × B; energy U = −m·B; stable at θ = 0°.
• Gauss’s law for magnetism: net flux through any closed surface is zero.
• B = μ₀(H + M); M = χH; μᵣ = 1 + χ.
• Diamagnetic χ is negative; paramagnetic χ is small and positive; ferromagnetic χ is large.
• Superconductor: χ = −1, perfect diamagnet (Meissner effect).
• Bismuth, copper, lead and water are diamagnetic; aluminium, sodium and oxygen are paramagnetic.
• Iron, cobalt, nickel and gadolinium are ferromagnetic.
• Alnico is a hard ferromagnet; soft iron is a soft ferromagnet.
• Above a high enough temperature, a ferromagnet becomes paramagnetic.
• Curie’s law (older edition): χ ∝ 1/T for paramagnets.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Thinking a magnet can be cut to isolate a north pole. Each piece is a complete magnet.
• Drawing magnetic field lines that start or end. They form closed loops, passing through the magnet from S to N inside.
• Expecting a net force on a magnet in a uniform field. Only a torque acts.
• Giving paramagnetic substances a negative susceptibility. Negative χ means diamagnetic.
• Saying only some substances show diamagnetism. It is present in all materials but often masked.
• Mixing up hard and soft ferromagnets. Hard ones (Alnico) keep their magnetism; soft iron loses it.
• Applying Curie’s law to diamagnets. It describes paramagnets, and the Curie temperature applies to ferromagnets.
• Confusing B and H units. B is in tesla; H and M are in A m⁻¹.

Magnetism and Matter Notes PDF and Related Pages

Download the AglaSem Class 12 Physics unit notes (Magnetic Effects of Current and Magnetism, and EMI and Alternating Current; key notes and important questions with answers) free: View PDF

• All chapters: Physics notes for NEET and JEE Main
• Full topic list: NEET syllabus and JEE Main syllabus
• Practice: NEET question papers and JEE Main question papers
• Source text: NCERT Chapter 5 (NCERT, Class 12 Physics Part I)

Physics Notes for NEET and JEE Main: All Chapters

• Units and Measurement
• Motion in a Straight Line
• Motion in a Plane
• Laws of Motion
• Work, Energy and Power
• Systems of Particles and Rotational Motion
• Gravitation
• Mechanical Properties of Solids
• Mechanical Properties of Fluids
• Thermodynamics
• Kinetic Theory of Gases
• Oscillations
• Waves
• Thermal Properties of Matter
• Electric Charges and Fields
• Electrostatic Potential and Capacitance
• Current Electricity
• Moving Charges and Magnetism
• Magnetism and Matter
• Electromagnetic Induction
• Electromagnetic Waves
• Ray Optics and Optical Instruments
• Wave Optics
• Dual Nature of Radiation and Matter
• Atoms
• Nuclei
• Semiconductor Electronics

All chapters with key points and notes PDFs are on the Physics notes for NEET and JEE Main page.

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