Magnetism and Matter — Class 12 MCQs with Answers

Magnetism and Matter — important questions & MCQs with answers (Class 12 Physics)

14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.

1. Q1Easy

   Magnetic monopoles:

   A.Are common

   B.Have not been observed✓ Correct

   C.Exist in iron

   D.Are positive only

   Answer: B. Have not been observed

   Explanation: Isolated N or S poles have never been observed — every magnet, however small, has both poles, which is why Gauss's law for magnetism gives ∮B·dA = 0, not μ₀q_m.

2. Q2Easy

   Iron, nickel, cobalt are:

   A.Ferromagnetic✓ Correct

   B.Diamagnetic

   C.Paramagnetic

   D.Non-magnetic

   Answer: A. Ferromagnetic

   Explanation: Fe, Ni, Co have unpaired electron spins that align into domains under a field, giving strong magnetisation (χ ~ 10³) — unlike paramagnets, this alignment survives as domains even without a field.

3. Q3Easy

   SI unit of magnetic dipole moment is:

   A.Henry

   B.Tesla

   C.Weber

   D.A·m²✓ Correct

   Answer: D. A·m²

   Explanation: m = IA, so its unit is ampere × metre² (A·m²) — don't confuse it with Tesla (unit of B) or Weber (unit of flux Φ = BA).

4. Q4Easy

   Magnetic susceptibility χ is defined by:

   A.M = χH✓ Correct

   B.B = χH

   C.H = χM

   D.χ = μ₀M

   Answer: A. M = χH

   Explanation: Magnetic susceptibility is defined through M = χH, a dimensionless ratio of induced magnetisation to applied field intensity — distinct from B = μ₀(H + M).

5. Q5Easy

   Magnetic field lines:

   A.Intersect freely

   B.Start at N and end nowhere

   C.Form closed loops✓ Correct

   D.Are straight always

   Answer: C. Form closed loops

   Explanation: Since no isolated magnetic pole exists, field lines never terminate — they form continuous closed loops, unlike electric field lines which start or end on charges.

6. Q6Easy

   Relative permeability μᵣ equals:

   A.χ − 1

   B.χ

   C.1 + χ✓ Correct

   D.1/χ

   Answer: C. 1 + χ

   Explanation: Since B = μ₀(H + M) = μ₀(1 + χ)H = μ₀μᵣH, comparing both forms gives μᵣ = 1 + χ directly.

7. Q7Medium

   Earth's magnetic dipole has its 'N' approximately at:

   A.Geographic North pole

   B.Geographic South pole✓ Correct

   C.Equator

   D.Centre

   Answer: B. Geographic South pole

   Explanation: Since opposite poles attract, a compass's north tip pointing toward geographic north means Earth's own dipole south pole sits near geographic north — so the dipole's north pole is near geographic south.

8. Q8Medium

   Diamagnetic materials are:

   A.Have no effect

   B.Strongly attracted

   C.Permanent magnets

   D.Weakly repelled by magnetic field✓ Correct

   Answer: D. Weakly repelled by magnetic field

   Explanation: Diamagnets develop an induced moment opposite to the applied field (χ < 0, small), so they are weakly repelled toward weaker-field regions — unlike paramagnets, which are weakly attracted.

9. Q9Medium

   A dipole of moment 0.5 A·m² in a field of 0.2 T at 30° experiences torque:

   A.0.05 N·m✓ Correct

   B.0.1 N·m

   C.0.01 N·m

   D.0.5 N·m

   Answer: A. 0.05 N·m

   Explanation: Torque on a dipole is τ = mB sinθ; here sin30° = 0.5, so τ = 0.5×0.2×0.5 = 0.05 N·m — the common slip is using cos30° instead of sin30°.

10. Q10Medium

    If χ = 499, relative permeability is:

    A.500✓ Correct

    B.498

    C.499

    D.1

    Answer: A. 500

    Explanation: μᵣ = 1 + χ = 1 + 499 = 500 — a direct substitution into the standard relation between relative permeability and susceptibility.

11. Q11Medium

    B at 0.1 m on axis of short bar magnet of m = 1 A·m²:

    A.2×10⁻³ T

    B.10⁻⁴ T

    C.10⁻³ T

    D.2×10⁻⁴ T✓ Correct

    Answer: D. 2×10⁻⁴ T

    Explanation: B_axial = (μ₀/4π)(2m/r³) = 10⁻⁷×2×1/(0.1)³ = 2×10⁻⁷/10⁻³ = 2×10⁻⁴ T — remember r³ in the denominator, not r².

12. Q12Hard

    Torque on magnetic dipole m in field B:

    A.mB²

    B.m·B

    C.m/B

    D.m × B✓ Correct

    Answer: D. m × B

    Explanation: Torque on a magnetic dipole is the vector cross product τ = m × B, magnitude mB sinθ, directed to align m with B — not the dot product m·B, which instead gives potential energy.

13. Q13Hard

    Above Curie temperature, ferromagnet becomes:

    A.Stronger

    B.Diamagnetic

    C.Paramagnetic✓ Correct

    D.Insulator

    Answer: C. Paramagnetic

    Explanation: Above the Curie temperature, thermal energy overcomes the exchange interaction that aligns domains, so the material loses spontaneous magnetisation and behaves as an ordinary paramagnet.

14. Q14Hard

    A magnet has time period T in B_H. If broken in half (cut perpendicular to length) and one piece oscillates in same B_H, new period:

    A.T

    B.T/2✓ Correct

    C.2T

    D.T/√2

    Answer: B. T/2

    Explanation: Cutting perpendicular to length halves both mass and length; since I ∝ ML², the piece's moment of inertia becomes I/8 while its moment m'=m/2 — as T ∝ √(I/m), T' = √((1/8)/(1/2))·T = T/2.

Magnetism and Matter — FAQs

More Class 12 Physics chapters

• 01Electric Charges and Fields
• 02Electrostatic Potential and Capacitance
• 03Current Electricity
• 04Moving Charges and Magnetism
• 06Electromagnetic Induction
• 07Alternating Current

Class 12 — other subjects

• Class 12 Biology chapters
• Class 12 Chemistry chapters
• Class 12 Computer Science chapters
• Class 12 English chapters
• Class 12 Mathematics chapters