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1. According to Gauss's Law in Magnetism, the net magnetic flux through any closed surface is always:
A. Positive
B. Negative
C. Zero
D. Infinite
Answer: C. Zero
Explanation: ∮ B · dA = 0 because isolated magnetic monopoles do not exist in nature; magnetic field lines always form continuous closed loops.
2. What happens when a bar magnet is cut into two equal halves perpendicular to its length?
A. Pole strength doubles, magnetic moment remains same
B. Pole strength remains same, magnetic moment becomes half
C. Both pole strength and magnetic moment become half
D. Magnetism is completely lost
Answer: B. Pole strength remains same, magnetic moment becomes half
Explanation: Cutting perpendicular to length halves the magnetic length (2l' = l), so new magnetic dipole moment M' = m × (l/2) = M / 2, while pole strength 'm' stays unchanged.
3. What is the relation between geometric length (L_g) and magnetic length (L_m) of a bar magnet?
A. L_m = L_g
B. L_m ≈ (5/6) L_g
C. L_m ≈ (6/5) L_g
D. L_m = 2 L_g
Answer: B. L_m ≈ (5/6) L_g
Explanation: Due to concentration of magnetic poles slightly inside physical ends, effective magnetic length is roughly 84% or 5/6th of its actual geometric length.
4. The magnetic field at a distance 'r' on the axial line of a short bar magnet varies as:
A. 1 / r
B. 1 / r²
C. 1 / r³
D. 1 / r⁴
Answer: C. 1 / r³
Explanation: For a short magnetic dipole, magnetic field on axial line is B_axis = (μ₀ / 4π) * (2M / r³), obeying an inverse cube distance relationship.
5. Ratio of magnetic field at a given distance 'r' on axial position to equatorial position for a short bar magnet is:
Answer: B. Ampere-meter² (A m²) or Joule/Tesla (J/T)
Explanation: Since M = I × A, its unit is Ampere × meter² (A m²). From U = -M·B, unit is also J/T.
7. The angle between Geographic Meridian and Magnetic Meridian at a place is called:
A. Angle of Dip (Inclination)
B. Angle of Declination
C. Horizontal component
D. Latitude
Answer: B. Angle of Declination
Explanation: Magnetic declination (α) is defined as the angle between true geographical north-south plane and magnetic north-south plane at a point on Earth.
8. What is the value of Angle of Dip (Inclination) at Earth’s magnetic equator and magnetic poles respectively?
A. 0° and 90°
B. 90° and 0°
C. 45° and 45°
D. 0° and 180°
Answer: A. 0° and 90°
Explanation: At magnetic equator, Earth's magnetic field is horizontal (Dip = 0°); at magnetic poles, field lines enter vertically (Dip = 90°).
9. Relation between total Earth magnetic field (B), horizontal component (B_H), and dip angle (δ) is:
A. B_H = B sinδ
B. B_H = B cosδ
C. B_H = B tanδ
D. B_H = B / cosδ
Answer: B. B_H = B cosδ
Explanation: Resolving total Earth's magnetic field B into components gives horizontal component B_H = B cosδ and vertical component B_V = B sinδ.
10. Susceptibility (χ) of Diamagnetic substances is:
A. Small and positive
B. Small and negative
C. Very large and positive
D. Zero
Answer: B. Small and negative
Explanation: Diamagnetic materials get weakly magnetized in direction opposite to applied field, giving a small negative magnetic susceptibility (-1 ≤ χ < 0).
11. Relative permeability (μ_r) of Paramagnetic materials is:
A. Less than 1
B. Slightly greater than 1
C. Equal to zero
D. Very much less than 0
Answer: B. Slightly greater than 1
Explanation: Paramagnetic materials attract magnetic lines weakly, so relative permeability μ_r = 1 + χ is slightly greater than 1.
12. Which class of magnetic materials displays Superdiamagnetism (perfect diamagnetism with χ = -1, μ_r = 0)?
A. Ferromagnetic metals
B. Superconductors
C. Ferrites
D. Insulators
Answer: B. Superconductors
Explanation: Superconductors expel magnetic field lines completely (Meissner effect), acting as perfect diamagnets with χ = -1 and μ_r = 0.
13. According to Curie's Law, magnetic susceptibility (χ) of a paramagnetic material varies with absolute temperature T as:
A. χ ∝ T
B. χ ∝ 1 / T
C. χ ∝ T²
D. χ is independent of T
Answer: B. χ ∝ 1 / T
Explanation: Curie's Law states magnetization decreases as thermal agitation increases, giving χ = C / T where C is Curie constant.
14. Curie Temperature is the temperature above which a ferromagnetic material transforms into:
A. Diamagnetic
B. Paramagnetic
C. Superconductor
D. Non-magnetic
Answer: B. Paramagnetic
Explanation: Above Curie temperature T_c, thermal energy destroys domain alignment, converting ferromagnetic behavior into paramagnetic behavior.
15. The domain theory is used to explain the magnetic properties of:
A. Diamagnetic materials
B. Paramagnetic materials
C. Ferromagnetic materials
D. All of these
Answer: C. Ferromagnetic materials
Explanation: Ferromagnetic materials consist of microscopic regions called domains where atomic dipole moments align spontaneously in a common direction.
16. The phenomenon of lagging of magnetic induction (B) behind magnetizing field (H) in ferromagnetic materials is called:
A. Hysteresis
B. Magnetic Flux
C. Resonance
D. Electromagnetic Induction
Answer: A. Hysteresis
Explanation: Hysteresis means "lagging behind". B lags behind H during magnetization and demagnetization cycles in ferromagnetic media.
17. Retentivity (or Remanence) of a magnetic material is defined as:
A. Residual magnetic field remaining when magnetizing field H = 0
B. Value of H required to make B zero
C. Maximum susceptibility value
D. Energy loss per cycle
Answer: A. Residual magnetic field remaining when magnetizing field H = 0
Explanation: Retentivity measures residual magnetization left in a specimen after external magnetizing force is reduced to zero.
18. Coercivity of a magnetic material is defined as:
A. Reverse magnetizing field required to reduce residual magnetism to zero
B. Saturation magnetization value
C. Permeability in free space
D. Magnetic moment per unit area
Answer: A. Reverse magnetizing field required to reduce residual magnetism to zero
Explanation: Coercivity represents reverse magnetizing intensity H_c required to completely wipe out residual magnetization in the material.
19. For making permanent magnets, the material should possess:
A. High retentivity and High coercivity
B. Low retentivity and Low coercivity
C. High retentivity and Low coercivity
D. Low retentivity and High coercivity
Answer: A. High retentivity and High coercivity
Explanation: Permanent magnets require high retentivity (strong remaining field) and high coercivity (resistant to demagnetization from stray fields or handling), like Steel or Alnico.
20. For making core of transformers and electromagnets, the material should possess:
A. High retentivity and High coercivity
B. High initial permeability, Low coercivity, and Low hysteresis loss
C. Low permeability and High hysteresis loss
D. High coercivity and High retentivity
Answer: B. High initial permeability, Low coercivity, and Low hysteresis loss
Explanation: Transformer cores undergo rapid AC magnetization cycles, needing low coercivity and narrow hysteresis loop area (e.g. Soft Iron) to minimize energy dissipation as heat.
21. The area of the Hysteresis Loop (B-H loop) represents:
A. Energy loss per unit volume per cycle of magnetization
B. Total magnetic flux
C. Permeability of the medium
D. Susceptibility of the sample
Answer: A. Energy loss per unit volume per cycle of magnetization
Explanation: Enclosed area of hysteresis loop directly measures energy dissipated as thermal heat per unit volume during one complete AC magnetization cycle.
22. Time period of oscillation (T) of a magnetic needle of moment M and moment of inertia I in uniform field B is:
A. T = 2π √(I / M B)
B. T = 2π √(M B / I)
C. T = 1 / (2π) √(I / M B)
D. T = 2π √(M / I B)
Answer: A. T = 2π √(I / M B)
Explanation: Restoring torque τ = -M B θ = I (d²θ/dt²). Solving simple harmonic motion equation yields T = 2π √(I / MB).
23. Water, Bismuth, Copper, and Gold belong to which magnetic category?
A. Ferromagnetic
B. Paramagnetic
C. Diamagnetic
D. Ferrimagnetic
Answer: C. Diamagnetic
Explanation: Substances like Bismuth, Copper, Water, Lead, and Gold are weakly repelled by magnets, exhibiting diamagnetism.
24. Aluminum, Sodium, Calcium, and Oxygen (at STP) are examples of:
A. Diamagnetic materials
B. Paramagnetic materials
C. Ferromagnetic materials
D. Non-magnetic elements
Answer: B. Paramagnetic materials
Explanation: Materials such as Aluminum, Sodium, Platinum, Chromium, and Manganese possess permanent atomic dipoles and show paramagnetism.
25. Tangent Law in magnetism, B = B_H tanθ, is applicable when a magnetic needle is under action of:
A. Single uniform magnetic field
B. Two mutually perpendicular uniform magnetic fields
C. Two parallel magnetic fields
D. Non-uniform electric fields
Answer: B. Two mutually perpendicular uniform magnetic fields
Explanation: Tangent Law states that if a compass needle comes to equilibrium at angle θ under two perpendicular fields B and B_H, then B = B_H tanθ.
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