Class 12 : Physics (English) – Chapter 5: Magnetism and Matter

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On June 25, 2025

EXPLANATION & SUMMARY

🌿 Introduction

Magnetism is one of the oldest and most fascinating natural phenomena. Ancient people discovered naturally magnetised iron ore, called lodestone, which had the property of attracting iron pieces. Later, this property was studied systematically and understood as the result of moving charges inside matter.

Every atom is like a miniature magnet because of two main sources of magnetic moment:

The orbital motion of electrons around the nucleus.

The intrinsic spin of electrons.

When these tiny magnetic moments add up in bulk, the material exhibits observable magnetism. This chapter focuses on bar magnets, the Earth’s magnetism, magnetic properties of materials, and hysteresis.

🔴 1. The Bar Magnet

Magnet bar isolated on white background illustration

A bar magnet has two poles: North pole and South pole.

Magnetic field lines emerge from the North pole and enter the South pole, forming closed loops inside the magnet.

Unlike electric charges, magnetic monopoles do not exist; poles always occur in pairs.

Bar and Horseshoe Magnets, Educational Magnetism Physics Science, Induction and Attraction. Compass Navigation Tool and Electromagnetic Field and Magnetic Force Schemes.

💡 Magnetic Dipole Moment (M):
M = m × 2l
where m is the pole strength and 2l is the distance between poles.

✔️ It is a vector quantity pointing from South pole to North pole.
✔️ SI Unit: A·m².

🟢 2. Magnetic Field of a Bar Magnet

The magnetic field due to a bar magnet resembles that of a magnetic dipole.

(a) Field at Axial Point

Consider a point on the axial line of the magnet at distance r from its centre.

Field due to North pole = μ₀m / (4π(r – l)²)

Field due to South pole = μ₀m / (4π(r + l)²)

Resultant field (for r >> l):
➡️ B_axial = (μ₀ / 4π) × (2M / r³)

(b) Field at Equatorial Point

On the equatorial line at distance r:

Field due to North pole = μ₀m / (4π(r² + l²))

Field due to South pole = same magnitude, opposite direction.

Resultant (for r >> l):
➡️ B_equatorial = (μ₀ / 4π) × (M / r³)

✔️ Thus, field varies inversely with r³, similar to an electric dipole.

🔴 3. Torque on a Bar Magnet in a Uniform Magnetic Field

When a bar magnet with dipole moment M is placed in a uniform external field B, it experiences:

Force: Zero (net force cancels).

Torque:
➡️ τ = MB sinθ
This tends to align the magnet with the external field.

💡 Potential Energy:
U = –M·B = –MB cosθ

✔️ Minimum energy occurs when the magnet aligns parallel to the external field.

🟢 4. Earth’s Magnetism

Earth behaves like a giant bar magnet with its magnetic axis tilted at about 11.3° to the geographical axis. The south magnetic pole lies near the geographic north, and vice versa.

Important Quantities:

Magnetic Declination (D): Angle between geographic meridian and magnetic meridian.

Magnetic Dip (I): Angle made by Earth’s magnetic field with the horizontal.

Horizontal component (Bh): Bh = B cos I.

Vertical component (Bv): Bv = B sin I.

✏️ Note: Navigators use correction for declination while using a magnetic compass.

🔴 5. Magnetisation and Magnetic Intensity

When a material is placed in a magnetic field, atomic dipoles tend to align.

✔️ Magnetisation (M):
M = (magnetic moment) / (volume)

✔️ Magnetic Intensity (H):
External magnetising field applied.

Relationship:
B = μ₀(H + M)

✔️ Magnetic Susceptibility (χm):
M = χm H

✔️ Permeability (μ):
B = μH, where μ = μ₀(1 + χm)

🟢 6. Magnetic Properties of Materials

Materials respond differently to applied magnetic fields:

(a) Diamagnetic

Weakly repelled by a magnetic field.

χm negative.

Example: Copper, Bismuth.

No magnetisation remains after field removal.

(b) Paramagnetic

Weakly attracted by a magnetic field.

χm small, positive.

Example: Aluminium, Platinum.

Magnetisation vanishes when field removed.

Strongly attracted, retain magnetisation.

χm very large, positive.

Example: Iron, Cobalt, Nickel.

Exhibit domain structure (regions of aligned dipoles).

✔️ Ferromagnets are widely used in technology (transformers, motors, magnetic recording).

🔴 7. Hysteresis Phenomenon

Ferromagnetic materials show magnetic hysteresis, meaning magnetisation does not vanish immediately when the external field is removed.

Hysteresis Loop (B–H curve):

O to A: Magnetisation increases with H.

A to B: Even when H → 0, magnetisation remains (retentivity).

B to C: Negative H needed to remove residual magnetisation (coercivity).

Loop area: Energy loss per cycle.

✔️ Retentivity: Determines suitability for permanent magnets.
✔️ Coercivity: Determines suitability for electromagnets.

🟢 8. Permanent Magnets vs Electromagnets

Permanent Magnet:

High retentivity and coercivity.

Example: Steel.

Electromagnet:

High permeability, low coercivity.

Example: Soft iron.

✔️ Electromagnets are used in cranes, relays, and MRI machines.

🔴 9. Magnetic Elements of Earth (Variations)

Secular variation: Gradual change in magnetic elements over centuries.

Diurnal variation: Daily change due to Earth’s rotation.

Magnetic storms: Disturbances due to solar activity.

These affect navigation and space communication.

🟢 10. Magnetic Dipole and Electric Dipole Analogy

Both have dipole moments.

Field ∝ 1/r³ at large distances.

Torque aligns them with the external field.

Difference: Electric monopoles exist, magnetic monopoles don’t.

🔴 11. Applications of Magnetism

Compass navigation (declination correction essential).

Motors and generators (electromagnets).

Transformers (soft iron cores).

Data storage (hard disks).

Medical imaging (MRI).

Security devices and credit card strips.

✔️ Magnetism finds wide applications in daily life and advanced technology.

🟡 Expanded Conceptual Depth Additions

Derivation of Torque Formula:
Consider a dipole of length 2l and pole strength m in field B.
Force on N pole = mB, on S pole = –mB.
Both forces form a couple → torque = mB × 2l sinθ = MB sinθ.

Energy in Magnetic Field:
Work done in rotating dipole from θ₁ to θ₂ = ∫ τ dθ = MB(cosθ₁ – cosθ₂).
So potential energy = –MB cosθ.

Hysteresis in practice:
In transformers, low energy loss (small loop) is desirable → soft iron.
For permanent magnets, large loop desirable → steel.

Earth’s Magnetic Field Estimation:
Gauss first measured it using deflection magnetometer.

🟢 Summary (~300 words)

Magnetism and Matter explains the magnetic behaviour of natural and artificial materials.

Bar Magnet: Acts like a dipole with moment M = m × 2l.

Magnetic Field:

Axial → (μ₀/4π)(2M/r³).

Equatorial → (μ₀/4π)(M/r³).

Torque & Energy: τ = MB sinθ, U = –MB cosθ.

Earth’s Magnetism: Earth is a tilted dipole; key elements: Declination (D), Dip (I), Bh = B cos I, Bv = B sin I.

Magnetisation & Intensity:

M = dipole moment/volume.

B = μ₀(H + M).

χm = M/H.

μ = μ₀(1 + χm).

Classification:

Diamagnetic (χm < 0).

Paramagnetic (χm > 0, small).

Ferromagnetic (χm large, positive).

Hysteresis Loop: Explains retentivity, coercivity, energy loss.

Magnets:

Permanent: steel (high retentivity).

Electromagnets: soft iron (low coercivity, high permeability).

Earth’s field variations: Secular, diurnal, magnetic storms.

Applications: Navigation, motors, generators, transformers, MRI, storage devices.

✔️ Thus, the chapter links microscopic origins of magnetism with macroscopic applications.

📝 Quick Recap

✔️ Bar magnet ≈ dipole (M = m × 2l).

✔️ B_axial ∝ 2M/r³, B_equatorial ∝ M/r³.

✔️ Torque = MB sinθ, U = –MB cosθ.

✔️ Earth’s magnetism → D, I, Bh, Bv.

✔️ Diamagnetic, paramagnetic, ferromagnetic.

✔️ Hysteresis → retentivity, coercivity, energy loss.

✔️ Permanent vs electromagnets.

✔️ Applications → compasses, transformers, MRI, data storage.

————————————————————————————————————————————————————————————————————————————

QUESTIONS FROM TEXTBOOK

Question 5.1
A short bar magnet placed with its axis at 30° with a uniform external magnetic field of 0.25 T experiences a torque of magnitude equal to 4.5 × 10⁻² J. What is the magnitude of magnetic moment of the magnet?
Answer
➡️ Given: τ = 4.5 × 10⁻² J, B = 0.25 T, θ = 30° (sinθ = 0.5)
✏️ Formula: τ = M B sinθ
🧠 Calculation: M = τ/(B sinθ) = (4.5 × 10⁻²)/(0.25 × 0.5) = 0.36 A·m²
✔️ Magnetic moment = 0.36 A·m²
Question 5.2
A short bar magnet of magnetic moment m = 0.32 J T⁻¹ is placed in a uniform magnetic field of 0.15 T. If the bar is free to rotate in the plane of the field, which orientation would correspond to (a) stable equilibrium and (b) unstable equilibrium? What is the potential energy of the magnet in each case?
Answer
➡️ Given: M = 0.32 J T⁻¹, B = 0.15 T
✏️ Potential energy: U = –MB cosθ
(a) Stable equilibrium → θ = 0° ⇒ U = –(0.32)(0.15)(1) = –0.048 J
(b) Unstable equilibrium → θ = 180° ⇒ U = –(0.32)(0.15)(–1) = +0.048 J
✔️ Stable at θ = 0°, unstable at θ = 180°.
Question 5.3
A closely wound solenoid of 800 turns and area of cross section 2.5 × 10⁻⁴ m² carries a current of 3.0 A. Explain the sense in which the solenoid behaves like a bar magnet. What is its associated magnetic moment?
Answer
➡️ Given: N = 800, A = 2.5 × 10⁻⁴ m², I = 3.0 A
✏️ Magnetic moment of a current loop/solenoid: M = N I A
🧠 Calculation: M = 800 × 3.0 × 2.5 × 10⁻⁴ = 0.60 A·m²
💡 The solenoid’s surface current produces a dipole moment; its ends act like N/S poles, so it behaves like a bar magnet with moment NIA.
Question 5.4
If the solenoid in Exercise 5.3 is free to turn about the vertical direction and a uniform horizontal magnetic field of 0.25 T is applied, what is the magnitude of torque on the solenoid when its axis makes an angle of 30° with the direction of field?
Answer
➡️ From Q5.3: M = 0.60 A·m²; B = 0.25 T; θ = 30°
✏️ τ = MB sinθ = 0.60 × 0.25 × 0.5 = 0.075 N·m
Question 5.5
A bar magnet of magnetic moment 1.5 J T⁻¹ lies aligned with the direction of a uniform magnetic field of 0.22 T.
(a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment (i) normal to the field, (ii) opposite to the field?
(b) What is the torque on the magnet in cases (i) and (ii)?
Answer
➡️ Given: M = 1.5 J T⁻¹, B = 0.22 T
✏️ Potential energy: U = –MB cosθ
(a) Work done = ΔU
(i) 0° → 90°: ΔU = [–MB cos90°] – [–MB cos0°] = 0 – (–MB) = MB = 0.33 J
(ii) 0° → 180°: ΔU = [–MB cos180°] – [–MB cos0°] = (+MB) – (–MB) = 2MB = 0.66 J
(b) Torque τ = MB sinθ
(i) At 90°: τ = MB = 0.33 N·m
(ii) At 180°: τ = 0 (since sin180° = 0)
Question 5.6
A closely wound solenoid of 2000 turns and area of cross-section 1.6 × 10⁻⁴ m², carrying a current of 4.0 A, is suspended through its centre allowing it to turn in a horizontal plane.
(a) What is the magnetic moment associated with the solenoid?
(b) What is the force and torque on the solenoid if a uniform horizontal magnetic field of 7.5 × 10⁻² T is set up at an angle of 30° with the axis of the solenoid?
Answer
➡️ Given: N = 2000, A = 1.6 × 10⁻⁴ m², I = 4.0 A, B = 7.5 × 10⁻² T, θ = 30°
(a) ✏️ M = N I A = 2000 × 4.0 × 1.6 × 10⁻⁴ = 1.28 A·m²
(b) ✔️ Net force on a dipole in a uniform field = 0
✏️ Torque: τ = MB sinθ = 1.28 × 7.5 × 10⁻² × 0.5 = 0.048 N·m
Question 5.7
A short bar magnet has a magnetic moment of 0.48 J T⁻¹. Give the direction and magnitude of the magnetic field produced by the magnet at a distance of 10 cm from the centre of the magnet on (a) the axis, (b) the equatorial lines (normal bisector) of the magnet.
Answer
➡️ Given: M = 0.48 J T⁻¹, r = 10 cm = 0.10 m; μ₀/4π = 1 × 10⁻⁷ T·m/A
✏️ Formulae:
Axial: B_axial = (μ₀/4π) × (2M / r³)
Equatorial: B_eq = (μ₀/4π) × (M / r³)
(a) Axial magnitude: B_axial = 10⁻⁷ × (2 × 0.48)/(0.1)³ = (0.96 × 10⁻⁷)/(10⁻³) = 9.6 × 10⁻⁵ T
🔎 Direction: Along the magnet’s axis in the same direction as the magnetic dipole moment (i.e., on the N-pole side, away from the magnet; outside, field lines are from N to S).
(b) Equatorial magnitude: B_eq = 10⁻⁷ × 0.48/(0.1)³ = (0.48 × 10⁻⁷)/(10⁻³) = 4.8 × 10⁻⁵ T
🔎 Direction: Along the equatorial line opposite to the magnetic dipole moment.

(CBSE MODEL QUESTIONS PAPER)

ESPECIALLY MADE FROM THIS LESSON ONLY

Section A (Q1–Q18: MCQs)

Question 1
Magnetic dipole moment of a bar magnet is defined as:
🔵 (A) Product of pole strength and distance between poles
🟢 (B) Product of pole strength and radius of atom
🟠 (C) Ratio of magnetic flux to pole strength
🔴 (D) Product of current and resistance
Answer: (A) Product of pole strength and distance between poles

Question 2
Unit of magnetic dipole moment in SI system is:
🔵 (A) Tesla
🟢 (B) A·m²
🟠 (C) Weber
🔴 (D) N·m
Answer: (B) A·m²

Question 3
Magnetic field along the axial line of a bar magnet at distance r is proportional to:
🔵 (A) 1/r
🟢 (B) 1/r²
🟠 (C) 1/r³
🔴 (D) r
Answer: (C) 1/r³

Question 4
For a bar magnet placed in a uniform field, maximum torque occurs when:
🔵 (A) Axis parallel to field
🟢 (B) Axis perpendicular to field
🟠 (C) Axis opposite to field
🔴 (D) Axis at any angle
Answer: (B) Axis perpendicular to field

Question 5
Potential energy of a magnetic dipole in uniform field is:
🔵 (A) MB cosθ
🟢 (B) –MB cosθ
🟠 (C) MB sinθ
🔴 (D) –MB sinθ
Answer: (B) –MB cosθ

Question 6
Earth’s magnetic dip is 0° at:
🔵 (A) Magnetic poles
🟢 (B) Magnetic equator
🟠 (C) Geographic poles
🔴 (D) Tropics
Answer: (B) Magnetic equator

Question 7
Earth’s magnetic dip is 90° at:
🔵 (A) Equator
🟢 (B) Geographic poles
🟠 (C) Magnetic poles
🔴 (D) Mid-latitudes
Answer: (C) Magnetic poles

Question 8
Which relation is correct?
🔵 (A) Bh = B sin I
🟢 (B) Bh = B cos I
🟠 (C) Bv = B cos I
🔴 (D) Bh = Bv tan I
Answer: (B) Bh = B cos I

Question 9
Diamagnetic materials are:
🔵 (A) Strongly repelled by field
🟢 (B) Weakly repelled by field
🟠 (C) Strongly attracted by field
🔴 (D) Retain magnetisation permanently
Answer: (B) Weakly repelled by field

Question 10
Magnetic susceptibility of paramagnetic materials is:
🔵 (A) Large positive
🟢 (B) Small positive
🟠 (C) Small negative
🔴 (D) Zero
Answer: (B) Small positive

Question 11
Which property characterises ferromagnets?
🔵 (A) Weak attraction by field
🟢 (B) Strong magnetisation retained even after field removal
🟠 (C) Always repelled by field
🔴 (D) Do not respond to field
Answer: (B) Strong magnetisation retained even after field removal

Question 12
Hysteresis loop area represents:
🔵 (A) Magnetic field strength
🟢 (B) Energy loss per cycle
🟠 (C) Torque
🔴 (D) Magnetic permeability
Answer: (B) Energy loss per cycle

Question 13
Material suitable for making electromagnets must have:
🔵 (A) High coercivity
🟢 (B) Low coercivity and high permeability
🟠 (C) High retentivity
🔴 (D) No susceptibility
Answer: (B) Low coercivity and high permeability

Question 14
Material suitable for making permanent magnets must have:
🔵 (A) Low retentivity and low coercivity
🟢 (B) High retentivity and high coercivity
🟠 (C) High susceptibility but low retentivity
🔴 (D) Small hysteresis loop area
Answer: (B) High retentivity and high coercivity

Question 15
If magnetic dipole is aligned anti-parallel to field, its potential energy is:
🔵 (A) Maximum positive
🟢 (B) Maximum negative
🟠 (C) Zero
🔴 (D) Infinite
Answer: (A) Maximum positive

Question 16
Which instrument works on Earth’s magnetism?
🔵 (A) Compass
🟢 (B) Barometer
🟠 (C) Thermometer
🔴 (D) Galvanometer
Answer: (A) Compass

Question 17
Which of the following is NOT ferromagnetic?
🔵 (A) Iron
🟢 (B) Nickel
🟠 (C) Cobalt
🔴 (D) Aluminium
Answer: (D) Aluminium

Question 18
Which of the following quantities is a vector?
🔵 (A) Magnetic intensity H
🟢 (B) Magnetic permeability μ
🟠 (C) Magnetic susceptibility χ
🔴 (D) Relative permeability μr
Answer: (A) Magnetic intensity H

Section B (Q19–Q23: Very Short Answer)

Question 19
Define magnetic declination.
Answer: Angle between geographic meridian and magnetic meridian.

Question 20
What is meant by magnetic dip or inclination?
Answer: Angle between Earth’s magnetic field and the horizontal plane at a place.

Question 21
What is the horizontal component of Earth’s magnetic field?
Answer: Bh = B cos I, the component of total field parallel to horizontal plane.

Question 22
Why is soft iron used to make electromagnets?
Answer: High permeability and low coercivity → easy to magnetise/demagnetise.

Question 23
Give two examples of ferromagnetic substances.
Answer: Iron, Cobalt, Nickel.

Section C (Q24–Q28: Mid-length)

Question 24
Derive torque on a bar magnet in a uniform field.
Answer: τ = MB sinθ (derived from couple of forces on poles).

Question 25
Derive potential energy of a dipole in uniform field.
Answer: U = –MB cosθ (obtained from work = ∫ τ dθ).

Question 26
A needle of dipole moment 0.02 A·m² in 0.002 T makes 60°. Find torque.
Answer: τ = MB sinθ = 0.02 × 0.002 × √3/2 = 3.46 × 10⁻⁵ N·m.

Question 27
Bar magnet: M = 1.2 J T⁻¹, B = 0.20 T, θ = 30°. Find (a) torque, (b) energy.
Answer:
(a) τ = MB sinθ = 0.12 N·m.
(b) U = –MB cosθ = –0.208 J.

Section D (Q28–Q31: Long Answer)

Question 28
Classification of magnetic materials.
Answer:

Diamagnetic (χ < 0, weakly repelled, e.g., Cu).

Paramagnetic (χ small +, weakly attracted, e.g., Al).

Ferromagnetic (χ large +, strongly attracted, domain structure, e.g., Fe).

Question 29
Hysteresis loop.
Answer:

Retentivity: residual magnetisation at H = 0.

Coercivity: reverse field to demagnetise.

Loop area = energy loss.
✔️ Applications: permanent magnets vs electromagnets.

Question 30
Derive field at axial point of bar magnet.
Answer:
B = (μ₀ / 4π) × [2M / r³] (for r >> l).

Question 31
Compare bar magnet and solenoid.
Answer:
Similarities: N/S poles, field patterns, dipole moment.
Differences: Magnet = atomic dipoles, solenoid = current; magnet fixed moment, solenoid adjustable.

Section E (Q32–Q33: Case/Application)

Question 32
Magnet (M = 0.5 A·m²) in Earth’s Bh = 3.6 × 10⁻⁵ T, rotated 0°→90°.
(a) Torque at 90° = MB = 1.8 × 10⁻⁵ N·m.
(b) Work = MB = 1.8 × 10⁻⁵ J.

Question 33
Which material for electromagnet vs permanent magnet?
Answer:

Electromagnets → soft iron (high μ, low coercivity).

Permanent magnets → steel/Alnico (high retentivity & coercivity).

NEET QUESTIONS FROM THIS LESSON

Question 1: The magnetic potential energy of a magnetic dipole is minimum when the angle between dipole moment and magnetic field is
🔵 (A) 0°
🟢 (B) 90°
🟠 (C) 180°
🔴 (D) 270°
Answer: (A) 0°
Year: 2025
Question 2: A diamagnetic substance is placed in an external magnetic field. Then lines of force are
🔵 (A) attracted towards it
🟢 (B) repelled away from it
🟠 (C) unaffected
🔴 (D) concentrate inside
Answer: (B) repelled away from it
Year: 2025
Question 3: For a paramagnetic substance, magnetic susceptibility (χ) varies with absolute temperature (T) as
🔵 (A) χ ∝ T
🟢 (B) χ ∝ 1/T
🟠 (C) χ ∝ 1/T²
🔴 (D) χ independent of T
Answer: (B) χ ∝ 1/T
Year: 2024
Question 4: Magnetic susceptibility is negative for
🔵 (A) ferromagnetic material
🟢 (B) diamagnetic material
🟠 (C) paramagnetic material
🔴 (D) all magnetic materials
Answer: (B) diamagnetic material
Year: 2024
Question 5: A bar magnet of magnetic moment M is cut into two equal halves along its length. The magnetic moment of each piece is
🔵 (A) M
🟢 (B) M/2
🟠 (C) 2M
🔴 (D) M/4
Answer: (B) M/2
Year: 2024
Question 6: At the magnetic equator, the angle of dip is
🔵 (A) 90°
🟢 (B) 0°
🟠 (C) 45°
🔴 (D) 60°
Answer: (B) 0°
Year: 2024
Question 7: Nickel shows ferromagnetic property at room temperature. If heated beyond its Curie temperature, it becomes
🔵 (A) diamagnetic
🟢 (B) paramagnetic
🟠 (C) antiferromagnetic
🔴 (D) non-magnetic
Answer: (B) paramagnetic
Year: 2023
Question 8: Which one of the following substances has small and negative magnetic susceptibility?
🔵 (A) Paramagnetic
🟢 (B) Ferromagnetic
🟠 (C) Diamagnetic
🔴 (D) Antiferromagnetic
Answer: (C) Diamagnetic
Year: 2023
Question 9: The tangent law of magnetism is used in
🔵 (A) vibration magnetometer
🟢 (B) tangent galvanometer
🟠 (C) moving coil galvanometer
🔴 (D) ballistic galvanometer
Answer: (B) tangent galvanometer
Year: 2023
Question 10: For a magnetised specimen, the relation between B, H and M is
🔵 (A) B = μ₀(H + M)
🟢 (B) B = μ₀HM
🟠 (C) B = μ₀(H − M)
🔴 (D) B = μ₀M
Answer: (A) B = μ₀(H + M)
Year: 2023
Question 11: A bar magnet placed in a uniform magnetic field experiences
🔵 (A) a torque only
🟢 (B) a net force only
🟠 (C) neither torque nor force
🔴 (D) both torque and force
Answer: (A) a torque only
Year: 2022
Question 12: The magnetic susceptibility of a paramagnetic material is
🔵 (A) large and negative
🟢 (B) small and positive
🟠 (C) large and positive
🔴 (D) small and negative
Answer: (B) small and positive
Year: 2022
Question 13: The magnetic moment of a current loop is proportional to
🔵 (A) current × radius
🟢 (B) current × area
🟠 (C) current/area
🔴 (D) 1/current
Answer: (B) current × area
Year: 2022
Question 14: Which type of material is used for making permanent magnets?
🔵 (A) Soft iron
🟢 (B) Steel
🟠 (C) Copper
🔴 (D) Aluminium
Answer: (B) Steel
Year: 2022
Question 15: Curie temperature is the temperature above which
🔵 (A) diamagnets become paramagnets
🟢 (B) ferromagnets become paramagnets
🟠 (C) paramagnets become diamagnets
🔴 (D) ferromagnets become non-magnetic
Answer: (B) ferromagnets become paramagnets
Year: 2021
Question 16: Which one has highest permeability?
🔵 (A) Diamagnetic
🟢 (B) Paramagnetic
🟠 (C) Ferromagnetic
🔴 (D) Non-magnetic
Answer: (C) Ferromagnetic
Year: 2021
Question 17: In Earth’s magnetism, the angle between true north and magnetic north is called
🔵 (A) declination
🟢 (B) inclination
🟠 (C) dip
🔴 (D) latitude
Answer: (A) declination
Year: 2021
Question 18: The unit of magnetic susceptibility is
🔵 (A) A/m
🟢 (B) Tesla
🟠 (C) dimensionless
🔴 (D) Weber
Answer: (C) dimensionless
Year: 2021
Question 19: The material suitable for making electromagnets should have
🔵 (A) high retentivity and high coercivity
🟢 (B) low retentivity and low coercivity
🟠 (C) high permeability and low coercivity
🔴 (D) low permeability and high coercivity
Answer: (C) high permeability and low coercivity
Year: 2020
Question 20: The hysteresis loss per cycle in a magnetic material is equal to
🔵 (A) area under B-H curve
🟢 (B) slope of B-H curve
🟠 (C) coercivity × retentivity
🔴 (D) μ₀HM
Answer: (A) area under B-H curve
Year: 2020
Question 21: The angle of dip at the magnetic poles is
🔵 (A) 0°
🟢 (B) 30°
🟠 (C) 45°
🔴 (D) 90°
Answer: (D) 90°
Year: 2020
Question 22: The magnetic intensity H is defined as
🔵 (A) B/μ₀ − M
🟢 (B) μ₀(B + M)
🟠 (C) B − μ₀M
🔴 (D) B/μ₀ + M
Answer: (A) B/μ₀ − M
Year: 2019
Question 23: At absolute zero, a ferromagnetic substance behaves as
🔵 (A) diamagnetic
🟢 (B) paramagnetic
🟠 (C) ferromagnetic
🔴 (D) antiferromagnetic
Answer: (C) ferromagnetic
Year: 2019
Question 24: A material with very large hysteresis loss is suitable for
🔵 (A) permanent magnets
🟢 (B) transformer cores
🟠 (C) electromagnets
🔴 (D) inductors
Answer: (A) permanent magnets
Year: 2019
Question 25: The dipole moment of a bar magnet is
🔵 (A) pole strength × length
🟢 (B) pole strength/length
🟠 (C) length/pole strength
🔴 (D) pole strength × area
Answer: (A) pole strength × length
Year: 2019
Question 26: Which quantity is zero inside a hollow magnetic shell?
🔵 (A) Magnetic intensity
🟢 (B) Magnetic flux
🟠 (C) Magnetic potential
🔴 (D) Magnetic induction
Answer: (D) Magnetic induction
Year: 2018
Question 27: For a ferromagnetic specimen, the initial susceptibility is
🔵 (A) small and positive
🟢 (B) large and positive
🟠 (C) negative
🔴 (D) zero
Answer: (B) large and positive
Year: 2018
Question 28: A bar magnet is equivalent to
🔵 (A) an electric dipole
🟢 (B) a solenoid of current
🟠 (C) a pair of charges
🔴 (D) a conductor with current
Answer: (B) a solenoid of current
Year: 2018
Question 29: The property of a material due to which it can withstand an external magnetic field without becoming permanently magnetised is best indicated by
🔵 (A) low coercivity
🟢 (B) high coercivity
🟠 (C) high susceptibility
🔴 (D) large retentivity
Answer: (A) low coercivity
Year: 2017
Question 30: The magnetic needle oscillates with period T in a magnetic field B. If field increases four times, new period is
🔵 (A) 2T
🟢 (B) T/2
🟠 (C) T/4
🔴 (D) 4T
Answer: (B) T/2
Year: 2017
Question 31: The value of magnetic inclination (dip) at a place where the horizontal component is equal to vertical component is
🔵 (A) 0°
🟢 (B) 30°
🟠 (C) 45°
🔴 (D) 90°
Answer: (C) 45°
Year: 2016
Question 32: In Earth’s magnetism, the angle between horizontal component and resultant magnetic field is
🔵 (A) declination
🟢 (B) dip
🟠 (C) latitude
🔴 (D) angle of elevation
Answer: (B) dip
Year: 2016
Question 33: The retentivity of a magnetic material is measure of
🔵 (A) energy stored
🟢 (B) magnetisation left when H = 0
🟠 (C) coercivity
🔴 (D) permeability
Answer: (B) magnetisation left when H = 0
Year: 2015
Question 34: A ferromagnetic material has
🔵 (A) very small susceptibility
🟢 (B) negative susceptibility
🟠 (C) very large susceptibility
🔴 (D) zero susceptibility
Answer: (C) very large susceptibility
Year: 2015
Question 35: The direction of earth’s magnetic field at a place makes an angle of 60° with horizontal. The vertical component if total intensity is 0.3 G, is
🔵 (A) 0.15 G
🟢 (B) 0.26 G
🟠 (C) 0.30 G
🔴 (D) 0.52 G
Answer: (B) 0.26 G
Year: 2015
Question 36: A diamagnetic rod is placed vertically between the poles of an electromagnet. When current is switched on, rod
🔵 (A) is pushed up
🟢 (B) is pushed down
🟠 (C) remains unaffected
🔴 (D) oscillates
Answer: (A) is pushed up
Year: 2014
Question 37: Which one of the following is not correctly matched?
🔵 (A) Soft iron – electromagnets
🟢 (B) Steel – permanent magnets
🟠 (C) Alnico – weak magnet
🔴 (D) Ferrite – transformer cores
Answer: (C) Alnico – weak magnet
Year: 2014
Question 38: In SI, unit of magnetic moment is
🔵 (A) Am²
🟢 (B) J/T
🟠 (C) Both (A) and (B)
🔴 (D) Tesla·m³
Answer: (C) Both (A) and (B)
Year: 2013
Question 39: The coercivity of a ferromagnetic material is
🔵 (A) high for soft iron
🟢 (B) high for steel
🟠 (C) zero
🔴 (D) same for all
Answer: (B) high for steel
Year: 2013
Question 40: When a bar magnet is cut into two equal halves perpendicular to its length, the pole strength of each part
🔵 (A) remains same
🟢 (B) doubles
🟠 (C) halves
🔴 (D) becomes zero
Answer: (A) remains same
Year: 2012
Question 41: The earth’s magnetic field at equator is
🔵 (A) vertical
🟢 (B) horizontal
🟠 (C) inclined 45°
🔴 (D) zero
Answer: (B) horizontal
Year: 2012
Question 42: The susceptibility of diamagnetic substance is
🔵 (A) small and positive
🟢 (B) large and positive
🟠 (C) small and negative
🔴 (D) large and negative
Answer: (C) small and negative
Year: 2011
Question 43: At Curie point, a ferromagnetic material becomes
🔵 (A) diamagnetic
🟢 (B) paramagnetic
🟠 (C) antiferromagnetic
🔴 (D) ferrimagnetic
Answer: (B) paramagnetic
Year: 2010
Question 44: Magnetic lines of force inside a bar magnet
🔵 (A) run from S to N
🟢 (B) run from N to S
🟠 (C) form open loops
🔴 (D) intersect each other
Answer: (A) run from S to N
Year: 2010
Question 45: The relative permeability μr and magnetic susceptibility χ are related as
🔵 (A) μr = 1 + χ
🟢 (B) μr = 1 − χ
🟠 (C) μr = χ
🔴 (D) μr = 1/χ
Answer: (A) μr = 1 + χ
Year: 2009
Question 46: The angle between magnetic meridian and geographic meridian is
🔵 (A) dip
🟢 (B) declination
🟠 (C) latitude
🔴 (D) longitude
Answer: (B) declination
Year: 2008
Question 47: Which is used for shielding from magnetic field?
🔵 (A) Copper
🟢 (B) Aluminium
🟠 (C) Soft iron
🔴 (D) Lead
Answer: (C) Soft iron
Year: 2007
Question 48: The magnetic susceptibility of a ferromagnet above Curie temperature
🔵 (A) is negative
🟢 (B) is small and positive
🟠 (C) is very large
🔴 (D) is zero
Answer: (B) is small and positive
Year: 2006
Question 49: The dipole moment of a bar magnet is doubled, its time period in vibration magnetometer will become
🔵 (A) doubled
🟢 (B) halved
🟠 (C) 1/√2 times
🔴 (D) √2 times
Answer: (C) 1/√2 times
Year: 2005
Question 50: The value of earth’s magnetic field is maximum at
🔵 (A) equator
🟢 (B) poles
🟠 (C) tropic of cancer
🔴 (D) tropic of capricorn
Answer: (B) poles
Year: 2004

JEE MAINS QUESTIONS FROM THIS LESSON

Part 1 (Q1–Q25)
Question 1: A bar magnet has magnetic moment M. It is divided into two equal parts lengthwise. The magnetic moment of each part is
🔵 (A) M/2
🟢 (B) M
🟠 (C) 2M
🔴 (D) 4M
Answer: (B) M
Year: 2025 | Shift 1
Question 2: The magnetic dipole moment of a solenoid of n turns, length l, area A, and current I is
🔵 (A) nIA
🟢 (B) n²IA
🟠 (C) nIl
🔴 (D) n²Il
Answer: (A) nIA
Year: 2025 | Shift 2
Question 3: A bar magnet placed in a uniform magnetic field experiences
🔵 (A) force only
🟢 (B) torque only
🟠 (C) both force and torque
🔴 (D) neither
Answer: (B) torque only
Year: 2024 | Shift 1
Question 4: The time period of freely suspended magnet is doubled. Its moment of inertia must be
🔵 (A) doubled
🟢 (B) halved
🟠 (C) quadrupled
🔴 (D) unchanged
Answer: (C) quadrupled
Year: 2024 | Shift 2
Question 5: The magnetic dipole moment of a current loop does not depend upon
🔵 (A) current
🟢 (B) area
🟠 (C) shape of loop
🔴 (D) number of turns
Answer: (C) shape of loop
Year: 2023 | Jan Shift 1
Question 6: If a magnet is cut into two equal pieces along its length, its pole strength
🔵 (A) doubles
🟢 (B) halves
🟠 (C) remains same
🔴 (D) becomes zero
Answer: (C) remains same
Year: 2023 | Apr Shift 2
Question 7: The earth’s magnetic field at a place has horizontal component 0.3 G and angle of dip 60°. The total intensity is
🔵 (A) 0.15 G
🟢 (B) 0.3 G
🟠 (C) 0.6 G
🔴 (D) 0.52 G
Answer: (D) 0.52 G
Year: 2022 | Jun Shift 1
Question 8: The magnetic susceptibility of a diamagnetic material is
🔵 (A) positive and small
🟢 (B) negative and small
🟠 (C) large and positive
🔴 (D) large and negative
Answer: (B) negative and small
Year: 2022 | Jul Shift 2
Question 9: The angle between magnetic meridian and geographic meridian is
🔵 (A) angle of dip
🟢 (B) angle of declination
🟠 (C) latitude
🔴 (D) longitude
Answer: (B) angle of declination
Year: 2022 | Jun Shift 2
Question 10: The time period of oscillation of a magnet in magnetic field B is proportional to
🔵 (A) 1/√B
🟢 (B) √B
🟠 (C) 1/B
🔴 (D) B
Answer: (A) 1/√B
Year: 2021 | Feb Shift 1
Question 11: The earth behaves as a magnet due to
🔵 (A) large deposits of iron
🟢 (B) rotation of earth
🟠 (C) convection currents in molten core
🔴 (D) gravitational field
Answer: (C) convection currents in molten core
Year: 2021 | Mar Shift 2
Question 12: A bar magnet is placed in a uniform magnetic field with its axis parallel. The force experienced is
🔵 (A) maximum
🟢 (B) minimum
🟠 (C) zero
🔴 (D) variable
Answer: (C) zero
Year: 2021 | Jul Shift 1
Question 13: The directive property of a magnet is due to
🔵 (A) Earth’s electric field
🟢 (B) Earth’s gravitational field
🟠 (C) Earth’s magnetic field
🔴 (D) Earth’s rotation
Answer: (C) Earth’s magnetic field
Year: 2020 | Jan Shift 1
Question 14: The unit of magnetic pole strength in SI is
🔵 (A) Ampere metre
🟢 (B) Weber
🟠 (C) Tesla
🔴 (D) Henry
Answer: (A) Ampere metre
Year: 2020 | Sept Shift 2
Question 15: A material with relative permeability < 1 is
🔵 (A) ferromagnetic
🟢 (B) diamagnetic
🟠 (C) paramagnetic
🔴 (D) ferrimagnetic
Answer: (B) diamagnetic
Year: 2020 | Sept Shift 1
Question 16: If BH curve of a material is narrow and small area, it is
🔵 (A) hard magnetic
🟢 (B) soft magnetic
🟠 (C) permanent magnet
🔴 (D) strong magnet
Answer: (B) soft magnetic
Year: 2019 | Jan Shift 2
Question 17: The unit of magnetic permeability is
🔵 (A) H/m
🟢 (B) Tm/A
🟠 (C) both A and B
🔴 (D) J/A²
Answer: (C) both A and B
Year: 2019 | Apr Shift 1
Question 18: A bar magnet has magnetic moment 0.4 J/T. It is placed in a uniform magnetic field of 0.16 T. The maximum torque is
🔵 (A) 0.064 Nm
🟢 (B) 0.032 Nm
🟠 (C) 0.16 Nm
🔴 (D) 0.04 Nm
Answer: (A) 0.064 Nm
Year: 2019 | Jan Shift 1
Question 19: The horizontal component of earth’s magnetic field at a place is 0.36 G. If dip angle is 30°, total magnetic field is
🔵 (A) 0.18 G
🟢 (B) 0.36 G
🟠 (C) 0.72 G
🔴 (D) 0.42 G
Answer: (C) 0.72 G
Year: 2019 | Apr Shift 2
Question 20: The substance with large positive susceptibility and hysteresis is
🔵 (A) diamagnetic
🟢 (B) paramagnetic
🟠 (C) ferromagnetic
🔴 (D) ferrimagnetic
Answer: (C) ferromagnetic
Year: 2018 | Jan
Question 21: Which of the following is not correct about magnetic lines of force?
🔵 (A) They form closed loops
🟢 (B) They start from N-pole and end at S-pole
🟠 (C) They intersect each other
🔴 (D) Tangent at a point gives direction of B
Answer: (C) They intersect each other
Year: 2018 | Apr
Question 22: The earth’s magnetic field is due to
🔵 (A) rotation of earth
🟢 (B) dynamo effect in core
🟠 (C) magnetic rocks
🔴 (D) atmospheric currents
Answer: (B) dynamo effect in core
Year: 2018
Question 23: The relation between magnetic induction B, magnetic field H, and magnetization M is
🔵 (A) B = μH
🟢 (B) B = μ₀(H + M)
🟠 (C) B = H + M
🔴 (D) B = μ₀H − M
Answer: (B) B = μ₀(H + M)
Year: 2017
Question 24: A diamagnetic material is placed in a magnetic field. It experiences
🔵 (A) force of attraction
🟢 (B) force of repulsion
🟠 (C) no force
🔴 (D) torque only
Answer: (B) force of repulsion
Year: 2017
Question 25: The work done in rotating a magnet of moment M in a uniform field B through an angle θ is
🔵 (A) MB(1 − cosθ)
🟢 (B) MB cosθ
🟠 (C) MB sinθ
🔴 (D) MB tanθ
Answer: (A) MB(1 − cosθ)
Year: 2017
Question 26: The unit of magnetic induction (B) in SI is
🔵 (A) Weber
🟢 (B) Tesla
🟠 (C) Gauss
🔴 (D) Ampere-turn/m
Answer: (B) Tesla
Year: 2017
Question 27: A magnetic needle suspended in a uniform magnetic field possesses potential energy minimum when angle between needle and field is
🔵 (A) 0°
🟢 (B) 90°
🟠 (C) 180°
🔴 (D) 45°
Answer: (A) 0°
Year: 2017
Question 28: A magnetic material has relative permeability slightly greater than 1. It is
🔵 (A) diamagnetic
🟢 (B) paramagnetic
🟠 (C) ferromagnetic
🔴 (D) ferrimagnetic
Answer: (B) paramagnetic
Year: 2016
Question 29: The instrument used to detect angle of dip is
🔵 (A) Dip circle
🟢 (B) Tangent galvanometer
🟠 (C) Fluxmeter
🔴 (D) Magnetometer
Answer: (A) Dip circle
Year: 2016
Question 30: The neutral point in the field of a bar magnet is the point where
🔵 (A) horizontal component of earth’s field is zero
🟢 (B) resultant of earth’s field and magnet’s field is zero
🟠 (C) dip angle is 90°
🔴 (D) vertical component of earth’s field is zero
Answer: (B) resultant of earth’s field and magnet’s field is zero
Year: 2016
Question 31: A magnetic needle is kept in a non-uniform magnetic field. It experiences
🔵 (A) torque only
🟢 (B) force only
🟠 (C) both torque and force
🔴 (D) neither
Answer: (C) both torque and force
Year: 2015
Question 32: Magnetic permeability of free space μ₀ is
🔵 (A) 4π × 10⁻⁷ H/m
🟢 (B) 9 × 10⁹ H/m
🟠 (C) 8.85 × 10⁻¹² H/m
🔴 (D) 1 H/m
Answer: (A) 4π × 10⁻⁷ H/m
Year: 2015
Question 33: The magnetic dipole moment of a bar magnet is
🔵 (A) product of pole strength and length
🟢 (B) ratio of pole strength and length
🟠 (C) square of pole strength
🔴 (D) ratio of pole strength and breadth
Answer: (A) product of pole strength and length
Year: 2015
Question 34: Which of the following is not a ferromagnetic material?
🔵 (A) Iron
🟢 (B) Cobalt
🟠 (C) Nickel
🔴 (D) Aluminium
Answer: (D) Aluminium
Year: 2015
Question 35: Magnetic susceptibility is negative for
🔵 (A) ferromagnetic materials
🟢 (B) diamagnetic materials
🟠 (C) paramagnetic materials
🔴 (D) none
Answer: (B) diamagnetic materials
Year: 2014
Question 36: The SI unit of magnetic dipole moment is
🔵 (A) A·m²
🟢 (B) Wb·m
🟠 (C) T·m
🔴 (D) J·m
Answer: (A) A·m²
Year: 2014
Question 37: The relation between B and H in a medium is
🔵 (A) B = μH
🟢 (B) B = H/μ
🟠 (C) B = μ/H
🔴 (D) B = Hμ²
Answer: (A) B = μH
Year: 2014
Question 38: Magnetic susceptibility χ is related to relative permeability μr as
🔵 (A) χ = μr − 1
🟢 (B) χ = 1/μr − 1
🟠 (C) χ = μr + 1
🔴 (D) χ = μr
Answer: (A) χ = μr − 1
Year: 2013
Question 39: The work done in turning a magnetic dipole of moment M through 180° in a uniform magnetic field B is
🔵 (A) 2MB
🟢 (B) MB
🟠 (C) zero
🔴 (D) MB/2
Answer: (A) 2MB
Year: 2013
Question 40: The angle between B and M in diamagnetic substance is
🔵 (A) 0°
🟢 (B) 90°
🟠 (C) 180°
🔴 (D) 45°
Answer: (C) 180°
Year: 2013
Question 41: A ferromagnetic substance above Curie temperature becomes
🔵 (A) paramagnetic
🟢 (B) diamagnetic
🟠 (C) non-magnetic
🔴 (D) superconducting
Answer: (A) paramagnetic
Year: 2012 (AIEEE)
Question 42: The relative permeability of free space is
🔵 (A) 0
🟢 (B) 1
🟠 (C) ∞
🔴 (D) μ₀
Answer: (B) 1
Year: 2012 (AIEEE)
Question 43: A freely suspended magnet oscillates with time period T. If its mass is doubled, then new time period is
🔵 (A) 2T
🟢 (B) T
🟠 (C) √2 T
🔴 (D) T/2
Answer: (B) T
Year: 2011 (AIEEE)
Question 44: If a bar magnet is cut into four equal parts along its length, the magnetic moment of each part is
🔵 (A) M/4
🟢 (B) M
🟠 (C) M/2
🔴 (D) 4M
Answer: (A) M/4
Year: 2011 (AIEEE)
Question 45: The coercivity of a material is large. The material is suitable for making
🔵 (A) permanent magnets
🟢 (B) electromagnets
🟠 (C) soft iron core
🔴 (D) transformer core
Answer: (A) permanent magnets
Year: 2010 (AIEEE)
Question 46: The area of B–H loop of a material gives
🔵 (A) permeability
🟢 (B) susceptibility
🟠 (C) energy loss per cycle
🔴 (D) retentivity
Answer: (C) energy loss per cycle
Year: 2010 (AIEEE)
Question 47: Which of the following has highest retentivity?
🔵 (A) Soft iron
🟢 (B) Steel
🟠 (C) Cobalt
🔴 (D) Nickel
Answer: (B) Steel
Year: 2009 (AIEEE)
Question 48: Magnetic lines of force due to a bar magnet are analogous to
🔵 (A) electric lines due to point charge
🟢 (B) equipotential surfaces
🟠 (C) lines of flow of liquid
🔴 (D) electric lines due to dipole
Answer: (D) electric lines due to dipole
Year: 2009 (AIEEE)
Question 49: The earth’s magnetic field is of the order of
🔵 (A) 10⁻² T
🟢 (B) 10⁻⁴ T
🟠 (C) 1 T
🔴 (D) 10 T
Answer: (B) 10⁻⁴ T
Year: 2008 (AIEEE)
Question 50: The pole strength of a bar magnet depends on
🔵 (A) length only
🟢 (B) material and cross-section
🟠 (C) shape only
🔴 (D) area only
Answer: (B) material and cross-section
Year: 2007 (AIEEE)

JEE ADVANCED QUESTIONS FROM THIS LESSON

Paper 1 (Q1–Q17)
Question 1: A magnetic dipole placed in a uniform magnetic field experiences
🔵 (A) only force
🟢 (B) only torque
🟠 (C) both torque and force
🔴 (D) neither
Answer: (B) only torque
Year: 2023 | Paper 1
Question 2: The magnetic susceptibility of a paramagnetic material varies with absolute temperature T as
🔵 (A) 1/T²
🟢 (B) 1/T
🟠 (C) T
🔴 (D) constant
Answer: (B) 1/T
Year: 2022 | Paper 1
Question 3: The intensity of magnetisation (I) is related to magnetic susceptibility (χ) and magnetising field (H) as
🔵 (A) I = H/χ
🟢 (B) I = χH
🟠 (C) I = H − χ
🔴 (D) I = χ/H
Answer: (B) I = χH
Year: 2022 | Paper 1
Question 4: Which of the following has highest permeability?
🔵 (A) Paramagnetic
🟢 (B) Ferromagnetic
🟠 (C) Diamagnetic
🔴 (D) Non-magnetic
Answer: (B) Ferromagnetic
Year: 2021 | Paper 1
Question 5: The work done in rotating a magnetic dipole of magnetic moment M by 90° in a uniform field B is
🔵 (A) MB
🟢 (B) 2MB
🟠 (C) MB/2
🔴 (D) zero
Answer: (A) MB
Year: 2021 | Paper 1
Question 6: Magnetic lines of force inside a bar magnet are directed from
🔵 (A) N to S
🟢 (B) S to N
🟠 (C) N to N
🔴 (D) random
Answer: (B) S to N
Year: 2020 | Paper 1
Question 7: SI unit of magnetic pole strength is
🔵 (A) A·m
🟢 (B) Wb
🟠 (C) T
🔴 (D) J/T
Answer: (A) A·m
Year: 2020 | Paper 1
Question 8: In diamagnetic substances, magnetic susceptibility is
🔵 (A) positive, small
🟢 (B) negative, small
🟠 (C) large, positive
🔴 (D) very large
Answer: (B) negative, small
Year: 2019 | Paper 1
Question 9: The coercivity of a soft iron specimen is
🔵 (A) large
🟢 (B) small
🟠 (C) zero
🔴 (D) infinite
Answer: (B) small
Year: 2019 | Paper 1
Question 10: If Earth’s magnetic field at a place is 40 μT and angle of dip is 60°, the vertical component is
🔵 (A) 20 μT
🟢 (B) 30 μT
🟠 (C) 40 μT
🔴 (D) 35 μT
Answer: (D) 35 μT
Year: 2018 | Paper 1
Question 11: Which one is a non-magnetic substance?
🔵 (A) Copper
🟢 (B) Iron
🟠 (C) Nickel
🔴 (D) Cobalt
Answer: (A) Copper
Year: 2018 | Paper 1
Question 12: Magnetic susceptibility of perfect diamagnetic material is
🔵 (A) 0
🟢 (B) −1
🟠 (C) 1
🔴 (D) ∞
Answer: (B) −1
Year: 2017 | Paper 1
Question 13: The unit of magnetic moment is
🔵 (A) A·m²
🟢 (B) J/T
🟠 (C) both A·m² and J/T
🔴 (D) none
Answer: (C) both A·m² and J/T
Year: 2017 | Paper 1
Question 14: The value of horizontal component of Earth’s magnetic field at equator is
🔵 (A) zero
🟢 (B) maximum
🟠 (C) minimum
🔴 (D) infinite
Answer: (B) maximum
Year: 2016 | Paper 1
Question 15: A magnetic needle is placed in a uniform field. Its moment of inertia is I and magnetic moment M. Time period is
🔵 (A) 2π√(M/IH)
🟢 (B) 2π√(I/MH)
🟠 (C) 2π√(H/MI)
🔴 (D) 2π√(IM/H)
Answer: (B) 2π√(I/MH)
Year: 2016 | Paper 1
Question 16: The phenomenon of temporary magnetisation is shown by
🔵 (A) soft iron
🟢 (B) steel
🟠 (C) alnico
🔴 (D) cobalt
Answer: (A) soft iron
Year: 2015 | Paper 1
Question 17: Permanent magnets are made of
🔵 (A) soft iron
🟢 (B) steel
🟠 (C) pure copper
🔴 (D) germanium
Answer: (B) steel
Year: 2015 | Paper 1

Paper 2 (Q18–Q34)
Question 18: The directive property of a magnet is due to
🔵 (A) Earth’s electric field
🟢 (B) Earth’s magnetic field
🟠 (C) rotation of Earth
🔴 (D) gravitational pull
Answer: (B) Earth’s magnetic field
Year: 2023 | Paper 2
Question 19: A solenoid of 1 m length has 1000 turns. Magnetic field inside, when carrying 2 A current, is (μ₀=4π×10⁻⁷)
🔵 (A) 2.51×10⁻³ T
🟢 (B) 2.51×10⁻² T
🟠 (C) 2.51×10⁻¹ T
🔴 (D) 2.51 T
Answer: (A) 2.51×10⁻³ T
Year: 2022 | Paper 2
Question 20: Torque on a magnet of magnetic moment 0.1 J/T in a field of 0.2 T at angle 60° is
🔵 (A) 0.01 Nm
🟢 (B) 0.02 Nm
🟠 (C) 0.017 Nm
🔴 (D) 0.05 Nm
Answer: (C) 0.017 Nm
Year: 2022 | Paper 2
Question 21: If χ = −10⁻⁵, the material is
🔵 (A) diamagnetic
🟢 (B) paramagnetic
🟠 (C) ferromagnetic
🔴 (D) ferrimagnetic
Answer: (A) diamagnetic
Year: 2021 | Paper 2
Question 22: In hysteresis loop, area enclosed represents
🔵 (A) susceptibility
🟢 (B) permeability
🟠 (C) energy loss per cycle
🔴 (D) retentivity
Answer: (C) energy loss per cycle
Year: 2021 | Paper 2
Question 23: A long bar magnet is cut into two equal halves (along its length). The magnetic moment of each piece is
🔵 (A) M
🟢 (B) M/2
🟠 (C) 2M
🔴 (D) zero
Answer: (B) M/2
Year: 2020 | Paper 2
Question 24: The value of Bohr magneton is
🔵 (A) 9.27×10⁻²⁴ A·m²
🟢 (B) 9.27×10⁻²⁴ J/T
🟠 (C) both (A) and (B)
🔴 (D) none
Answer: (C) both (A) and (B)
Year: 2020 | Paper 2
Question 25: A magnetic material has relative permeability μr < 1. It is
🔵 (A) paramagnetic
🟢 (B) diamagnetic
🟠 (C) ferromagnetic
🔴 (D) none
Answer: (B) diamagnetic
Year: 2019 | Paper 2
Question 26: The direction of Earth’s magnetic field inside Earth is
🔵 (A) S → N
🟢 (B) N → S
🟠 (C) downward
🔴 (D) upward
Answer: (A) S → N
Year: 2019 | Paper 2
Question 27: If work done to rotate a magnetic needle from parallel to perpendicular is W, then work done from perpendicular to antiparallel is
🔵 (A) W
🟢 (B) 2W
🟠 (C) 3W
🔴 (D) 4W
Answer: (A) W
Year: 2018 | Paper 2
Question 28: Which material is used for making permanent magnets?
🔵 (A) Soft iron
🟢 (B) Steel
🟠 (C) Copper
🔴 (D) Aluminium
Answer: (B) Steel
Year: 2018 | Paper 2
Question 29: Which type of magnetisation curve shows hysteresis?
🔵 (A) Ferromagnetic
🟢 (B) Diamagnetic
🟠 (C) Paramagnetic
🔴 (D) Non-magnetic
Answer: (A) Ferromagnetic
Year: 2017 | Paper 2
Question 30: If dip angle is 90°, horizontal component is
🔵 (A) maximum
🟢 (B) zero
🟠 (C) minimum
🔴 (D) infinite
Answer: (B) zero
Year: 2017 | Paper 2
Question 31: If magnetic field at equator is H, then field at poles is
🔵 (A) H
🟢 (B) H/2
🟠 (C) 2H
🔴 (D) zero
Answer: (C) 2H
Year: 2016 | Paper 2
Question 32: The law of force between two poles is similar to
🔵 (A) Coulomb’s law
🟢 (B) Ohm’s law
🟠 (C) Faraday’s law
🔴 (D) Ampere’s law
Answer: (A) Coulomb’s law
Year: 2016 | Paper 2
Question 33: The unit of intensity of magnetisation is
🔵 (A) A/m
🟢 (B) A·m²
🟠 (C) T
🔴 (D) Wb/m²
Answer: (A) A/m
Year: 2015 | Paper 2
Question 34: Magnetic susceptibility of ferromagnetic substance above Curie temperature is
🔵 (A) negative
🟢 (B) constant
🟠 (C) 1/T
🔴 (D) 1/T²
Answer: (C) 1/T
Year: 2015 | Paper 2

PRACTICE SETS FROM THIS LESSON

🔵 NEET Level (Q1–Q20)

Q1. Magnetic dipole moment of a bar magnet depends on:
🔵 (A) Magnetic pole strength only
🟢 (B) Length of the magnet only
🟠 (C) Product of pole strength and pole separation
🔴 (D) Magnetic field in which it is placed
Answer: (C) Product of pole strength and pole separation

Q2. SI unit of magnetic moment is:
🔵 (A) J/T
🟢 (B) A·m²
🟠 (C) Tesla
🔴 (D) Weber
Answer: (B) A·m²

Q3. A bar magnet’s field is most similar to:
🔵 (A) Uniform electric field
🟢 (B) Dipole electric field
🟠 (C) Circular field around a wire
🔴 (D) Uniform gravitational field
Answer: (B) Dipole electric field

Q4. Torque on a dipole is maximum when angle between M and B is:
🔵 (A) 0°
🟢 (B) 90°
🟠 (C) 180°
🔴 (D) 45°
Answer: (B) 90°

Q5. Potential energy of dipole aligned parallel to field:
🔵 (A) Maximum positive
🟢 (B) Maximum negative
🟠 (C) Zero
🔴 (D) Infinite
Answer: (B) Maximum negative

Q6. Potential energy difference between parallel and antiparallel alignment =
🔵 (A) MB
🟢 (B) 2MB
🟠 (C) MB/2
🔴 (D) Zero
Answer: (B) 2MB

Q7. Declination at a place is 0° when:
🔵 (A) Magnetic meridian = Geographic meridian
🟢 (B) Magnetic dip = 0°
🟠 (C) Bh = Bv
🔴 (D) Earth’s field is zero
Answer: (A) Magnetic meridian = Geographic meridian

Q8. At magnetic equator, the value of dip is:
🔵 (A) 0°
🟢 (B) 45°
🟠 (C) 60°
🔴 (D) 90°
Answer: (A) 0°

Q9. At magnetic poles, horizontal component Bh is:
🔵 (A) Maximum
🟢 (B) Zero
🟠 (C) Equal to B
🔴 (D) Undefined
Answer: (B) Zero

Q10. Which is diamagnetic?
🔵 (A) Iron
🟢 (B) Nickel
🟠 (C) Copper
🔴 (D) Cobalt
Answer: (C) Copper

Q11. Paramagnetic susceptibility (χm) is:
🔵 (A) Large negative
🟢 (B) Small positive
🟠 (C) Zero
🔴 (D) Infinite
Answer: (B) Small positive

Q12. Ferromagnetism is due to:
🔵 (A) Random alignment of dipoles
🟢 (B) Domain structure
🟠 (C) Diamagnetic shielding
🔴 (D) Absence of magnetic dipoles
Answer: (B) Domain structure

Q13. Hysteresis loop area gives:
🔵 (A) Energy gained
🟢 (B) Energy lost per cycle
🟠 (C) Magnetic flux density
🔴 (D) Permeability
Answer: (B) Energy lost per cycle

Q14. Suitable material for transformer core:
🔵 (A) Steel
🟢 (B) Soft iron
🟠 (C) Copper
🔴 (D) Aluminium
Answer: (B) Soft iron

Q15. Permanent magnets require:
🔵 (A) Low coercivity
🟢 (B) High retentivity and coercivity
🟠 (C) Low permeability
🔴 (D) High conductivity
Answer: (B) High retentivity and coercivity

Q16. Earth’s field at equator:
🔵 (A) Vertical
🟢 (B) Horizontal
🟠 (C) Zero
🔴 (D) At 45°
Answer: (B) Horizontal

Q17. Direction of dipole moment vector in magnet:
🔵 (A) From North → South
🟢 (B) From South → North
🟠 (C) From centre outward
🔴 (D) Along field lines
Answer: (B) From South → North

Q18. Magnetic susceptibility (χm) relation with μr:
🔵 (A) μr = 1 + χm
🟢 (B) μr = 1 – χm
🟠 (C) μr = χm
🔴 (D) μr = χm/μ₀
Answer: (A) μr = 1 + χm

Q19. Which law explains torque on magnet in uniform field?
🔵 (A) Ampere’s law
🟢 (B) Biot-Savart law
🟠 (C) Dipole law
🔴 (D) Couple law
Answer: (C) Dipole law

Q20. In ferromagnetic material, domains align when:
🔵 (A) Heated
🟢 (B) Magnetic field applied
🟠 (C) Pressure applied
🔴 (D) Kept in dark
Answer: (B) Magnetic field applied

🟢 JEE Main Level (Q21–Q40)

Q21. A dipole of moment 0.1 A·m² in 0.2 T at 60°. Torque?
🔵 (A) 0.01 N·m
🟢 (B) 0.017 N·m
🟠 (C) 0.02 N·m
🔴 (D) 0
Answer: (B) 0.017 N·m

Q22. A magnet in field has U = –MB cosθ. At θ = 90°, U =
🔵 (A) –MB
🟢 (B) 0
🟠 (C) +MB
🔴 (D) –2MB
Answer: (B) 0

Q23. For axial point, field ratio to equatorial point at same r is:
🔵 (A) 1:1
🟢 (B) 2:1
🟠 (C) 1:2
🔴 (D) 4:1
Answer: (B) 2:1

Q24. At r = 0.1 m, M = 0.2 A·m², B_axial = ?
🔵 (A) 2 × 10⁻⁴ T
🟢 (B) 4 × 10⁻⁵ T
🟠 (C) 2 × 10⁻⁵ T
🔴 (D) 4 × 10⁻⁴ T
Answer: (A) 2 × 10⁻⁴ T

Q25. A 1000-turn solenoid, I = 2 A, area = 1 × 10⁻⁴ m². Dipole moment?
🔵 (A) 0.2 A·m²
🟢 (B) 0.1 A·m²
🟠 (C) 0.05 A·m²
🔴 (D) 0.4 A·m²
Answer: (A) 0.2 A·m²

Q26. Retentivity of steel compared to soft iron is:
🔵 (A) Smaller
🟢 (B) Larger
🟠 (C) Same
🔴 (D) Zero
Answer: (B) Larger

Q27. Which curve area is smallest (least energy loss)?
🔵 (A) Steel
🟢 (B) Alnico
🟠 (C) Soft iron
🔴 (D) Cobalt
Answer: (C) Soft iron

Q28. If dip = 45°, then Bh : Bv =
🔵 (A) 1:1
🟢 (B) √3:1
🟠 (C) 1:√3
🔴 (D) 0:1
Answer: (A) 1:1

Q29. Work done rotating dipole 180° in field:
🔵 (A) MB
🟢 (B) 2MB
🟠 (C) MB/2
🔴 (D) Zero
Answer: (B) 2MB

Q30. Which shows Curie’s law (χ ∝ 1/T)?
🔵 (A) Diamagnet
🟢 (B) Paramagnet
🟠 (C) Ferromagnet
🔴 (D) Superconductor
Answer: (B) Paramagnet

Q31. If χm = –10⁻⁵, material is:
🔵 (A) Para
🟢 (B) Ferro
🟠 (C) Dia
🔴 (D) None
Answer: (C) Dia

Q32. If μr = 1000, substance is:
🔵 (A) Para
🟢 (B) Ferro
🟠 (C) Dia
🔴 (D) Non-magnetic
Answer: (B) Ferro

Q33. Net force on dipole in uniform B:
🔵 (A) MB
🟢 (B) Zero
🟠 (C) τ
🔴 (D) B/μ₀
Answer: (B) Zero

Q34. Which increases magnetisation on heating?
🔵 (A) Diamagnet
🟢 (B) Paramagnet
🟠 (C) Ferromagnet
🔴 (D) None
Answer: (A) Diamagnet

Q35. Above Curie temperature, ferromagnets behave as:
🔵 (A) Para
🟢 (B) Dia
🟠 (C) Ferro
🔴 (D) Non-magnetic
Answer: (A) Para

Q36. A dipole in stable equilibrium has:
🔵 (A) θ = 0°
🟢 (B) θ = 90°
🟠 (C) θ = 180°
🔴 (D) Any angle
Answer: (A) θ = 0°

Q37. Which is used for permanent magnets?
🔵 (A) Steel
🟢 (B) Soft iron
🟠 (C) Copper
🔴 (D) Aluminium
Answer: (A) Steel

Q38. A material has large coercivity. It is used for:
🔵 (A) Electromagnet
🟢 (B) Transformer core
🟠 (C) Permanent magnet
🔴 (D) Alloys
Answer: (C) Permanent magnet

Q39. Earth’s field lines emerge:
🔵 (A) From South magnetic pole to North magnetic pole
🟢 (B) From North magnetic pole to South magnetic pole
🟠 (C) From equator to poles
🔴 (D) Random
Answer: (A) From South to North magnetic pole (inside Earth, opposite outside).

Q40. In SI, magnetic field B is measured in:
🔵 (A) A/m
🟢 (B) Tesla
🟠 (C) Weber
🔴 (D) J/T
Answer: (B) Tesla

🔴 JEE Advanced Level (Q41–Q50)

Q41. A magnet of moment M in field B at θ has energy:
🔵 (A) –MB cosθ
🟢 (B) MB cosθ
🟠 (C) –MB sinθ
🔴 (D) MB sinθ
Answer: (A) –MB cosθ

Q42. Work done rotating dipole from 30° → 60°:
🔵 (A) MB(√3/2 – √3/2)
🟢 (B) MB(cos30° – cos60°)
🟠 (C) MB(cos60° – cos30°)
🔴 (D) MB sin30°
Answer: (B) MB(cos30° – cos60°)

Q43. Ratio of axial to equatorial field at r:
🔵 (A) 1
🟢 (B) 2
🟠 (C) 3
🔴 (D) 4
Answer: (B) 2

Q44. A bar magnet is cut into two halves along length. Magnetic moment:
🔵 (A) Halved
🟢 (B) Doubled
🟠 (C) Same
🔴 (D) Becomes zero
Answer: (A) Halved

Q45. If χ = 1000, μr = ?
🔵 (A) 1
🟢 (B) 1001
🟠 (C) 1000
🔴 (D) 0
Answer: (B) 1001

Q46. Temperature dependence of χ for paramagnet:
🔵 (A) χ ∝ T
🟢 (B) χ ∝ 1/T
🟠 (C) χ ∝ T²
🔴 (D) Independent
Answer: (B) χ ∝ 1/T

Q47. At θ = 45°, torque vs potential energy relation?
🔵 (A) τ = U
🟢 (B) τ > U
🟠 (C) τ < U
🔴 (D) No relation
Answer: (C) τ < U (since U = –MB cosθ, τ = MB sinθ).

Q48. A small magnet free to rotate makes frequency f in Earth’s field B. Doubling B makes frequency:
🔵 (A) f
🟢 (B) 2f
🟠 (C) √2 f
🔴 (D) f/2
Answer: (B) 2f

Q49. Curie temperature is the temperature:
🔵 (A) Above which paramagnet → dia
🟢 (B) Above which ferromagnet → paramagnet
🟠 (C) Below which diamagnet → paramagnet
🔴 (D) Where χ = 0 for all
Answer: (B) Above which ferromagnet → paramagnet

Q50. For maximum retentivity, hysteresis loop must be:
🔵 (A) Narrow and tall
🟢 (B) Wide and tall
🟠 (C) Narrow and short
🔴 (D) Wide and short
Answer: (B) Wide and tall

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