- Which of the following materials is not attracted by a magnet?
A) Iron
B) Nickel
C) Copper
D) Cobalt
Answer: C) Copper
Explanation: Only ferromagnetic, paramagnetic materials are attracted by magnets. Copper is diamagnetic and weakly repels (or shows negligible attraction). - Magnetic field lines are always closed loops. True or False?
A) True
B) False
Answer: A) True
Explanation: Magnetic field lines emerge from the north pole and return to the south outside the magnet; inside the magnet they go from south to north, making closed loops. There are no magnetic monopoles. - What is the SI unit of magnetic flux?
A) Tesla
B) Weber
C) Ampere
D) Henry
Answer: B) Weber
Explanation: Magnetic flux is measured in Weber (Wb). Tesla measures magnetic flux density. - If a magnetic dipole of pole strength
and separation 
has a dipole moment 
, then 
?
A)
B)
C)
D)
Answer: B)
Explanation: Magnetic dipole momentpole strength × length of the dipole. - Which of these is not a property of magnetic lines of force?
A) They never intersect each other
B) They are closed loops
C) They start from south pole and end at north pole outside magnet
D) They indicate direction of magnetic field
Answer: C) They start from south pole and end at north pole outside magnet
Explanation: Outside a magnet, lines emerge from north pole and end at south pole. The option C is reversed. - A charge moving with velocity through a magnetic field
experiences force . Which relation is correct?
A)
B)
C)
D)
Answer: B)
Explanation: Lorentz force; the magnetic force on a moving charge is vector product of velocity and magnetic field. Works only when velocity and B are not parallel. - Work done by magnetic force on a moving charged particle is …
A) Maximum
B) Depends on B
C) Depends on speed of particle
D) Zero
Answer: D) Zero
Explanation: Magnetic force is always perpendicular to velocity; therefore, no work is done (force does not change kinetic energy). - What happens to the magnetic field inside a long solenoid if current through it increases?
A) It decreases
B) It remains same
C) It increases
D) It reverses direction
Answer: C) It increases
Explanation: Magnetic field in solenoid is proportional to current (for fixed number of turns). Thus, increasing current increases magnetic field. - Which of the following materials has negative magnetic susceptibility?
A) Paramagnetic
B) Diamagnetic
C) Ferromagnetic
D) Antiferromagnetic
Answer: B) Diamagnetic
Explanation: Diamagnetic materials develop magnetization opposite to the applied field → negative susceptibility. - The Curie point of a ferromagnetic material is …
A) The temperature below which it becomes diamagnetic
B) The temperature above which it loses ferromagnetism
C) The temperature at which magnetic susceptibility is zero
D) The temperature at which relative permittivity becomes unity
Answer: B) The temperature above which it loses ferromagnetism
Explanation: Beyond the Curie temperature, thermal agitation destroys domain alignment; it behaves paramagnetically. - Magnetic intensity
in vacuum is related to magnetic flux density by:
A)
B)
C)
D)
Answer: A)
Explanation: In vacuum⇒ . - Intensity of magnetization (magnetization
) is defined as:
A) Magnetic moment per unit current
B) Magnetic moment per unit volume
C) Magnetic moment per unit area
D) Magnetic moment per unit length
Answer: B) Magnetic moment per unit volume
Explanation:where is magnetic moment, is volume. - Which of these is not correct for paramagnetic materials?
A) Relative permeability > 1
B) Susceptibility > 0
C) They retain magnetization without external field
D) They are weakly attracted by magnetic field
Answer: C) They retain magnetization without external field
Explanation: That’s a property of ferromagnetics. Paramagnetics lose alignment once external field removed. - What is the angle of dip at a place where horizontal component of Earth’s magnetic field equals vertical component?
A) 45°
B) 0°
C) 90°
D) 60°
Answer: A) 45°
Explanation: When horizontal = vertical component → tan(dip) = 1 → dip = 45°. - A magnetic needle is placed in a non‑uniform magnetic field, what forces/torques act on it?
A) Only torque
B) Only force
C) Both force and torque
D) Neither force nor torque
Answer: C) Both force and torque
Explanation: Non‑uniform field exerts net force (pull toward region of stronger field) and torque (attempt to align with field). - What does hysteresis in a ferromagnetic material represent?
A) The instantaneous magnetization
B) The lag between magnetization and magnetizing field
C) The alignment of domains
D) The point where magnetization becomes zero
Answer: B) The lag between magnetization and magnetizing field
Explanation: When field cycles, magnetization lags behind, giving a loop (hysteresis). Energy is lost. - If a bar magnet is broken into two halves, what happens?
A) You get a north pole in one piece, a south pole in other
B) Each piece has both north and south poles
C) You get only north poles in both pieces
D) Poles disappear
Answer: B) Each piece has both north and south poles
Explanation: Magnetic poles always appear in pairs; you cannot isolate a magnetic monopole by breaking a bar magnet. - Magnetic susceptibility
and relative permeability 
of a diamagnetic substance satisfy:
A)
B)
C)
D)
Answer: A)
Explanation: Diamagnetism gives negative susceptibility; relative permeability slightly less than one. - Which law states that the induced electromotive force (EMF) in a circuit is proportional to the rate of change of magnetic flux through the circuit?
A) Ampere’s Law
B) Ohm’s Law
C) Faraday’s Law
D) Lenz’s Law
Answer: C) Faraday’s Law
Explanation: Faraday’s law quantifies induced EMF = −dΦ/dt. Lenz’s law gives direction of induced current. - Which of the following is used to measure strength of magnetic field?
A) Ammeter
B) Voltmeter
C) Gaussmeter
D) Thermometer
Answer: C) Gaussmeter
Explanation: A Gaussmeter (or magnetometer) is used to measure magnetic flux density.
- The ratio of intensity of magnetisation (magnetisation) to magnetising force is known as
A) Flux density
B) Susceptibility
C) Relative permeability
D) None of the above
Answer: B) Susceptibility
Explanation: Magnetic susceptibility (χ) = (Intensity of magnetisation) / (Magnetising force). - A uniform magnetic field is one in which
A) The field of a set of parallel conductors
B) The field of a single conductor
C) The field in which all lines of magnetic flux are parallel and equidistant
D) None of the above
Answer: C) The field in which all lines of magnetic flux are parallel and equidistant
Explanation: Uniform field means same magnitude & direction everywhere; flux lines parallel & equidistant. - Stray lines of magnetic flux are those which:
A) are vertical to the flux lines
B) are the mean length of a ring shaped coil
C) lie in a non‑uniform field
D) do not follow the designed path
Answer: D) A line of magnetic flux which does not follow the designed path
Explanation: Stray flux is unwanted magnetic flux that escapes core or designed magnetic circuit. - Magnetic reluctance of a material:
A) Decreases with increasing cross‑sectional area of material
B) Increases with increasing cross‑sectional area of material
C) Does not vary with increasing cross‑sectional area of material
D) Any of the above
Answer: A) Decreases with increasing cross‑sectional area of material
Explanation: Reluctance, analog of resistance in magnetics, is inversely proportional to cross sectional area. Larger area lowers reluctance. - The unit of pole strength is same as unit of:
A) Reluctance
B) Resistance
C) Permeance
D) Pole strength
Answer: D) Pole strength
Explanation: Sometimes pole strength is quoted in units like Am (ampere‑meter) or similar; but more properly unit of pole strength is “Am”). In that MCQ, they meant comparing units. - Magnetic moment is a:
A) Pole strength
B) Universal constant
C) Scalar quantity
D) Vector quantity
Answer: D) Vector quantity
Explanation: Magnetic moment has both magnitude and direction (from south to north for a bar magnet). - Core of an electromagnet should have:
A) Low coercivity
B) High susceptibility
C) Both of the above
D) None of the above
Answer: C) Both of the above
Explanation: Low coercivity means it can be magnetised and demagnetised easily (reduce hysteresis loss); high susceptibility means it gets large magnetisation for small magnetising force—makes electromagnet strong. - Which part of a magnetic path requires largest magnetomotive force (m.m.f.)?
A) Air gap
B) Coil
C) Inductance
D) Core
Answer: A) Air gap
Explanation: Because air has very low permeability, so a gap in magnetic circuit greatly increases reluctance, requiring larger m.m.f. to maintain flux. - Strength of an electromagnet can be increased by:
A) Increasing the cross‐sectional area
B) Increasing the number of turns
C) Increasing current supply
D) All of the above
Answer: D) All of the above
Explanation: Larger area reduces reluctance; more turns increases magnetomotive force; more current also increases the magnetising force. - A permanent magnet:
A) Attracts some substances and repels others
B) Attracts all paramagnetic substances and repels others
C) Attracts only ferromagnetic substances
D) Attracts ferromagnetic substances and repels all others
Answer: A) Attracts some substances and repels others
Explanation: Some substances like ferromagnetic are attracted; diamagnetic are weakly repelled; paramagnetic weakly attracted; behaviour differs. - The relative permeability of which materials is not constant?
A) Diamagnetic
B) Paramagnetic
C) Ferromagnetic
D) Insulating
Answer: C) Ferromagnetic
Explanation: Ferromagnetic materials have permeability that depends strongly on applied field strength; i.e., permeability is not linear and not constant. - Ferrites are a subgroup of:
A) Non‑magnetic materials
B) Ferromagnetic materials
C) Paramagnetic materials
D) Ferri‑magnetic materials
Answer: D) Ferri‑magnetic materials
Explanation: Ferrites are ferrimagnetic – some magnetic moments cancel partially, giving net moment; have properties between ferromagnetic and antiferromagnetic. - Degaussing is the process of:
A) Removal of magnetic impurities
B) Removing gases from the materials
C) Remagnetising metallic parts
D) Demagnetising metallic parts
Answer: D) Demagnetising metallic parts
Explanation: Degaussing means reducing or eliminating a magnetic field or magnetisation. - In the Left Hand Rule (Fleming’s left hand rule), the forefinger always represents:
A) Voltage
B) Current
C) Magnetic field
D) Direction of force on the conductor
Answer: C) Magnetic field
Explanation: In Fleming’s left hand rule: Thumb = Force (motion), Forefinger = Magnetic field, Middle finger = Current. - The tubes of force within the magnetic material are known as:
A) Electric flux
B) Lines of force
C) Tubes of indication
D) None of the above
Answer: B) Lines of force
Explanation: “Lines of force” refer to magnetic flux lines or tubes of magnetic flux. - The Biot‑Savart’s law is a general modification of:
A) Kirchhoff’s law
B) Lenz’s law
C) Ampere’s law
D) Faraday’s laws
Answer: C) Ampere’s law
Explanation: Biot‑Savart’s law gives magnetic field due to infinitesimal current element; Ampere’s law is integral form; sometimes Biot‐Savart is considered more general (applies always) while Ampere’s works under symmetry. - The magnetic materials exhibit magnetisation because of:
A) Orbital motion of electrons
B) Spin of electrons
C) Spin of nucleus
D) All of the above
Answer: D) All of the above
Explanation: Magnetic moments arise from both spin and orbital motion of electrons; nucleus’s contribution is negligible but existent in precise theory. - For which materials the saturation value is the highest?
A) Ferromagnetic materials
B) Paramagnetic materials
C) Diamagnetic materials
D) Ferrites
Answer: D) Ferrites
Explanation: Ferrites can have high saturation flux densities; depends on material; in many engineering magnets, ferrites achieve high performance. (Though some ferromagnetic metals have very high saturation too; but in context, ferrites are cited.) - For which materials the net magnetic moment should be zero?
A) Diamagnetic materials
B) Ferrimagnetic materials
C) Antiferromagnetic materials
D) Antiferrimagnetic materials
Answer: C) Antiferromagnetic materials
Explanation: In antiferromagnetic materials, adjacent magnetic moments are equal and opposite, cancelling out; net = 0. - Which of the following has low value in ferrites?
A) Conductivity
B) Permeability
C) Magnetic susceptibility
D) All the above
Answer: A) Conductivity
Explanation: Ferrites are good insulators (low conductivity), used in high frequency applications to reduce eddy currents; their permeability and susceptibility are reasonable.
- Two identical bar magnets each of dipole moment M and length l are placed perpendicular to each other. The resultant dipole moment is:
A) √2 M
B) 2 M
C) M/√2
D) M/2
Answer: A) √2 M
Explanation: Vector addition of two perpendicular equal dipoles gives resultant magnitude = M√2. - Hysteresis loop for a material of permanent magnet should be:
A) long and thin
B) short and thin
C) short and wide
D) long and wide
Answer: D) long and wide
Explanation: For permanent magnets, you want large coercivity & remanence → wide loop, and large area (long) to retain magnetisation. - A steel wire of length l has magnetic moment M. It is bent into a semicircular arc. The new magnetic moment is:
A) M / l
B) M
C) 2M / π
D) M × l
Answer: C) (2/π) M
Explanation: If originally wire carrying current I with area enclosed for straight wire vs semi‑circular, the area changes, giving factor of 2/π. - The unit of magnetic flux is:
A) Ohm
B) Weber
C) Tesla
D) None of the above
Answer: B) Weber
Explanation: SI unit of magnetic flux (Φ) is Weber (Wb). Tesla is unit of magnetic flux density (B). - The angle of dip at a place where horizontal component equals vertical component is:
A) 45°
B) 0°
C) 90°
D) 30°
Answer: A) 45°
Explanation: If horizontal component H = vertical component V, tan(dip) = V / H = 1 → dip = 45°. - Isoclinic lines are lines joining places of:
A) equal dip
B) equal declination
C) 0° dip and 90° declination
D) equal dip & declination both
Answer: A) equal dip
Explanation: “Isoclinic” means same inclination/dip. “Isogonic” would refer to declination. - A magnetic dipole moment is a vector quantity directed from:
A) South to North pole
B) North to South pole
C) East to West
D) West to East
Answer: A) South to North pole
Explanation: By convention, dipole moment vector points from south pole toward north pole inside the magnet. - Tangent law is applicable only when:
A) Two uniform and mutually perpendicular magnetic fields exist
B) Two magnetic fields exist
C) Horizontal component of Earth’s field is present
D) Uniform magnetic field are used
Answer: A) Two uniform and mutually perpendicular magnetic fields exist
Explanation: Tangent law (for magnetic needle) gives relation between resultant & component fields when two fields are perpendicular & uniform. - The magnetic field in the empty space enclosed by a toroidal solenoid of radius R is:
A) Infinity
B) μ₀/(4π) * 2πlR (some expression)
C) μ₀/(4π) (π l R)
D) Zero
Answer: D) Zero
Explanation: In an ideal toroidal solenoid, magnetic field outside the coils (including the space in the centre) is zero (if tightly wound, neglecting leakage). - The dimensional representation of magnetic flux density B is:
A) [MLT⁻²]
B) [MLT⁻² A⁻¹]
C) [MLT⁻² A⁻²]
D) [MT⁻² A⁻¹]
Answer: D) [M T⁻² A⁻¹]
Explanation: Using SI: Tesla = N / (A·m) = (kg·m/s²) / (A·m) = kg / (s²·A). That yields [M T⁻² A⁻¹]. - A magnetic bar of moment M placed in field of strength B, the torque acting is:
A) M · B (dot)
B) – M · B
C) M × B
D) B × M
Answer: C) M × B
Explanation: Torque τ = magnetic moment vector × magnetic field vector. Direction from right hand rule. - In Physics, a neutral point in the magnetic field of a horizontally placed bar magnet (immersed in Earth’s field) is a point where the magnetic field due to the bar magnet is:
A) zero
B) more than that of Earth
C) less than that of Earth
D) equal to that of Earth
Answer: D) equal to that of Earth
Explanation: At neutral point, fields of Earth & magnet cancel → magnitudes equal. - In a moving coil galvanometer, one uses radial magnetic field so that the scale is:
A) exponential
B) linear
C) algebraic
D) logarithmic
Answer: B) linear
Explanation: Radial field ensures torque proportional to current and deflection proportional to current → linear scale. - On quadrupling the moment of inertia of a magnet, its frequency of oscillation will become:
A) half
B) double
C) four times
D) one‑fourth
Answer: A) half
Explanation: For oscillating magnet, frequency f ∝ 1/√I (I = moment of inertia). If I → 4I, then f → (1/2) original. Gurukul of Excellence - The magnetic field strength due to a short bar magnet directed along its axial line at distance r is B. What is its value at same distance along the equatorial line?
A) B
B) 2B
C) B/2
D) B/4
Answer: C) B/2
Explanation: For bar magnet, along equatorial line, field is half of axial field (magnitude) if distances same. - The force between two parallel wires in vacuum is 2×10⁻⁷ N m⁻¹ when currents and distance given. If placed 1 m apart and force per metre is that, current is:
A) 1 A
B) zero
C) 5×10⁶ A
D) 2×10⁻⁷ A
Answer: A) 1 A
Explanation: Ampère’s force law: F/L = (μ₀ I₁ I₂)/(2π d). Using values gives I = 1 A. - What is magnetic field of Earth due to:
A) Induction effect of sun
B) The presence of a large magnet at centre of Earth
C) Interaction of cosmic rays with current of Earth
D) Motion and distribution of some material in and outside the Earth
Answer: D) Motion and distribution of some material in and outside the Earth
Explanation: Earth’s magnetic field arises from dynamo effect – motion of conducting fluids in outer core, etc. Not literally a big permanent magnet. - The radius of curvature of the path of a charged particle in a uniform magnetic field is directly proportional to:
A) charge on the particle
B) momentum of particle
C) energy of particle
D) strength of field
Answer: B) momentum of particle
Explanation: In magnetic field, for circular motion, radius r = p / (qB). So r ∝ momentum. - A wire of length l has magnetic moment M. It is bent into a semi‑circular arc. The new magnetic moment is: (repeat type)
A) M
B) M × l
C) 2M / π
D) M / π
Answer: C) 2M / π
Explanation: As earlier (Q43). - Which of these has higher magnetic susceptibility?
A) Diamagnetic
B) Paramagnetic
C) Ferromagnetic
D) None of these
Answer: C) Ferromagnetic
Explanation: Ferromagnetic materials have very large positive susceptibility. Diamagnetic have negative small value; paramagnetic small positive.
- The unit of magnetic flux is Weber. The unit of magnetic flux density is:
A) Weber
B) Tesla
C) Ampere
D) Henry
Answer: B) Tesla
Explanation: Flux density B = flux per unit area; its unit = Wb/m² = Tesla (T). - Which of the following materials is diamagnetic?
A) Iron
B) Aluminium
C) Graphite
D) Nickel
Answer: C) Graphite
Explanation: Diamagnetic materials weakly repel magnetic fields; graphite is diamagnetic. - The magnetic intensity H in vacuum is related to magnetic flux density B by:
A) H = B / μ₀
B) H = μ₀ B
C) H = B² / μ₀
D) H = µ₀² B
Answer: A) H = B / μ₀
Explanation: In vacuum, B = μ₀ H ⇒ H = B/μ₀. - Which is correct relation for magnetic susceptibility χ, relative permeability μ_r?
A) χ < 0, μ_r < 1 (diamagnetic)
B) χ > 0, μ_r > 1 (paramagnetic)
C) χ >> 1 for ferromagnets
D) All of the above
Answer: D) All of the above
Explanation: Diamagnetic: negative χ, μ_r <1; paramagnetic: small positive; ferromagnetic: very large positive. - In a bar magnet, the magnetic lines of force:
A) start from North and end at South outside
B) start from South and end at North outside
C) circular paths from middle
D) continuous through magnet & outside
Answer: A) start from North and end at South outside
Explanation: Outside magnet lines emerge from North, outside → South, and inside South → North to complete loop. - Magnetic field inside a long straight solenoid carrying current I, with n turns per length, is given by:
A) μ₀ I / n
B) μ₀ n I
C) B = μ₀ I² n
D) B = (I × n) / μ₀
Answer: B) μ₀ n I
Explanation: For ideal infinitely long solenoid, B = μ₀ (turns per unit length) × current. - Work done by magnetic force on moving charged particle is:
A) positive
B) depends on angle
C) zero
D) negative
Answer: C) zero
Explanation: Magnetic force always perpendicular to velocity ⇒ no work done (kinetic energy unchanged). - What happens if a bar magnet is broken into two halves?
A) You get a north pole in one piece, a south in the other
B) Each piece has both north and south poles
C) You get only north poles in both pieces
D) Poles disappear
Answer: B) Each piece has both north and south poles
Explanation: Magnetic poles always come in pairs; breaking gives smaller magnets with both poles. - Which law states induced EMF in any closed circuit is equal to the rate of change of magnetic flux through the circuit?
A) Ampere’s law
B) Ohm’s law
C) Faraday’s law
D) Lenz’s law
Answer: C) Faraday’s law
Explanation: Faraday’s law: ε = −dΦ/dt; Lenz gives direction. - The coercivity of a magnetic material is:
A) Field required to reduce surance to zero
B) Field required to reduce permeability to zero
C) Field required to reduce magnetisation to zero after saturation
D) Field required to saturate the material
Answer: C) Field required to reduce magnetisation to zero after saturation
Explanation: Coercive field is negative field needed to bring magnetisation back to zero after saturation. - Magnetic saturation means:
A) All magnetic domains aligned
B) No further increase in magnetisation with increased field
C) Further increase in field won’t increase B significantly
D) All of above
Answer: D) All of above
Explanation: When nearly all domains aligned, magnetisation saturates; further increase in field produces very little increase. - Relative permeability μ_r is defined as:
A) B / μ₀ H
B) H / (μ₀ B)
C) B / H
D) μ / μ₀
Answer: D) μ / μ₀
Explanation: Relative permeability = permeability of material divided by permeability of free space. - The magnetising force H inside a solenoid:
A) Independent of current
B) Proportional to current & turns / length
C) Proportional to square of current
D) Zero
Answer: B) Proportional to current & turns / length
Explanation: H = (N I)/l for solenoid (ignoring end effects). - Diamagnetic materials have:
A) Negative susceptibility, weakly repelled by magnets
B) Zero susceptibility, no response
C) Positive large susceptibility, strongly attracted
D) Susceptibility depends strongly on temperature
Answer: A) Negative susceptibility, weakly repelled by magnets
Explanation: Diamagnetism arises due to induced magnetisation opposite to applied field. - Paramagnetic materials:
A) Retain magnetisation when field removed
B) Become strongly magnetised
C) Are weakly attracted by magnetic field and lose magnetisation when field removed
D) Repelled by magnets
Answer: C) Are weakly attracted by magnetic field and lose magnetisation when field removed
Explanation: Paramagnetics have positive susceptibility but slight and temporary. - Which statement about ferromagnetism is false?
A) There exist magnetic domains
B) There is strong dependence of magnetisation on temperature
C) Permeability is independent of field strength
D) They show hysteresis
Answer: C) Permeability is independent of field strength
Explanation: For ferromagnets, permeability depends on field; it changes as magnetisation curve moves into saturation. - Curie temperature is the temperature:
A) At which ferromagnets become superconductors
B) Above which ferromagnets lose their ferromagnetism
C) At which susceptibility becomes zero
D) Below which materials become diamagnetic
Answer: B) Above which ferromagnets lose their ferromagnetism
Explanation: At Curie point, thermal agitation overcomes aligning forces, material becomes paramagnetic. - Magnetic susceptibility of paramagnetic material varies with temperature as per Curie’s law:
A) χ ∝ T
B) χ ∝ 1/T
C) χ ∝ T²
D) χ independent of T
Answer: B) χ ∝ 1/T
Explanation: Curie’s law: χ = C / T (for ideal paramagnets). - In antiferromagnetic materials, at very low temperatures:
A) Net magnetisation is large
B) Magnetic moments align parallel
C) Net magnetisation is zero
D) They behave like ferromagnets
Answer: C) Net magnetisation is zero
Explanation: Opposing spins cancel out. - Ferrimagnetic materials differ from antiferromagnetic materials because:
A) In ferri, opposing moments are unequal → net moment
B) In antiferro, opposing moments equal → net zero
C) Ferrites (a class of ferrimagnetic) have high resistivity
D) All of above
Answer: D) All of above
Explanation: These are defining features; ferrimagnetic materials (like ferrites) have unbalanced opposing moments, giving net magnetisation; good resistivity helps reduce eddy losses.
- The Earth’s magnetic field lines emerge from which pole geographically?
A) North Pole
B) South Pole
C) Magnetic North
D) Magnetic South
Answer: B) South Pole (geographic)
Explanation: Earth’s magnetic South geographic pole is close to the magnetic north pole, from where field lines emerge. Note: geographic terms vs magnetic terminology can be confusing. - Declination in Earth’s magnetic field means:
A) Angle between magnetic meridian and geographic meridian
B) Angle of dip
C) Horizontal component of field
D) Vertical component of field
Answer: A) Angle between magnetic meridian and geographic meridian
Explanation: Declination is the angle by which compass needle deviates from geographic north. - Magnetic dip means:
A) Angle between magnetic field line and horizontal at a point
B) Deviation of needle from magnetic meridian
C) Vertical component of earth’s field
D) Horizontal component of field
Answer: A) Angle between magnetic field line and horizontal at a point
Explanation: The inclination or dip of Earth’s field. - The magnetisation (M) of a material is defined as:
A) Magnetic moment per unit mass
B) Magnetic moment per unit volume
C) Field strength times susceptibility
D) Magnetic flux density per unit volume
Answer: B) Magnetic moment per unit volume
Explanation: Magnetisation is M = magnetic moment / volume. - The B‑H curve of a soft magnetic material has:
A) Large coercivity and large retentivity
B) Small coercivity and small hysteresis loop area
C) Large coercivity and small hysteresis loop area
D) Small coercivity but wide loop
Answer: B) Small coercivity and small hysteresis loop area
Explanation: Soft material should respond easily, minimal energy loss, low coercivity & narrow hysteresis loop. - A coil carrying current in a magnetic field experiences torque when placed:
A) parallel to field
B) perpendicular to field
C) at any angle ≠ 0° or 180°
D) always zero torque
Answer: C) at any angle ≠ 0° or 180°
Explanation: Torque τ = NIBA sinθ; maximum when perpendicular, zero when parallel/antiparallel. - If current through a solenoid is reversed, then magnetic field inside:
A) remains same
B) reverses direction
C) doubles
D) becomes zero
Answer: B) reverses direction
Explanation: Direction of magnetic field depends on current direction (via right hand rule). - Magnetic field at center of circular loop of radius R carrying current I is given by:
A) μ₀ I / 2R
B) μ₀ I / (2π R)
C) μ₀ I² / 2R
D) μ₀ 2I / R
Answer: A) μ₀ I / (2R)
Explanation: For circular loop, B = μ₀ I / (2R) at centre. - Energy stored in magnetic field in an inductor of inductance L with current I is:
A) ½ LI²
B) LI²
C) ½ L² I
D) L² I²
Answer: A) ½ L I²
Explanation: Standard energy formula for inductor. - A small current loop in a uniform magnetic field B with magnetic moment M has potential energy U = −M ⋅ B. If moment aligned with field, U is:
A) Minimum (‑MB)
B) Maximum (+MB)
C) Zero
D) Indeterminate
Answer: A) Minimum (‑MB)
Explanation: Potential energy lowest when dipole moment aligned with field; U = −MB. - The magnetising field inside a magnetic material is reduced due to:
A) Demagnetising field
B) External applied field
C) Thermal agitation
D) Saturation
Answer: A) Demagnetising field
Explanation: Inside real magnetic samples, demagnetising fields oppose applied field, reducing effective magnetising field. - Remanence in magnetic material is:
A) Field required to demagnetise completely
B) Magnetisation retention when the magnetising field is removed
C) Maximum magnetisation possible
D) Zero magnetisation after removing field
Answer: B) Magnetisation retention when the magnetising field is removed
Explanation: Remanent magnetisation is what stays after external field goes to zero. - In a given material, hysteresis loss is proportional to:
A) Coercivity² × frequency
B) Area of hysteresis loop × frequency
C) Permeability × frequency
D) Coercivity × remanence × current
Answer: B) Area of hysteresis loop × frequency
Explanation: Energy loss per cycle = area of loop; total loss ∝ area × number of cycles per second. - Which kind of magnet has high coercivity, high retentivity, used for permanent magnets:
A) Soft iron
B) Alnico alloys
C) Silicon steel
D) Mumetal
Answer: B) Alnico alloys
Explanation: Alnico is used for permanent magnet materials because of high coercivity & good retentivity. - The demagnetising effect is strongest in:
A) long cylinder magnetised along length
B) thin disc magnetised perpendicular to plane
C) sphere
D) ring (toroid)
Answer: B) thin disc magnetised perpendicular to plane
Explanation: Demagnetising factors depend on shape; thin flat disc has high demagnetizing factor in that direction. - The magnetic field at a point equidistant from two unlike poles (north & south) along the line joining them is:
A) Zero
B) Increases away from mid‑point
C) At mid‑point, field is strong & directed from north to that point
D) At mid‑point, field is directed from south to north
Answer: A) Zero
Explanation: Along equidistant line between unlike poles, the fields are equal in magnitude and opposite in direction, thus cancel. - The magnetic field due to an infinite straight current‑carrying wire at a distance r is proportional to:
A) 1/r
B) 1/r²
C) r
D) constant
Answer: A) 1/r
Explanation: B = μ₀ I / (2π r) for infinite straight wire → inversely proportional to distance. - A bar magnet is suspended at a place where the dip is 60°, it oscillates with frequency f. If moved to place where dip is 30°, oscillation frequency becomes:
A) f
B) f × √2
C) f / √2
D) f × 2
Answer: B) f × √2
Explanation: Frequency ∝ √(B_horizontal component) since restoring torque depends on horizontal component; if dip reduces from 60° to 30°, horizontal component increases → frequency increases by factor √2. - A magnetic compass needle oscillates 30 times/min at a place with dip 45°, and 40 times/min at a place with dip 30°. If B₁ and B₂ are total magnetic fields at these two places, then B₁/B₂ is approximately:
A) 3.6
B) 0.7
C) 2.2
D) 1.8
Answer: D) 1.8
Explanation: Frequency of oscillation ω ∝ √(mgh / I) × (horizontal component of magnetic field / M) etc. Using ratio and dip angles, get ~1.8. - A magnet when brought close to three needles N1 (ferromagnetic), N2 (paramagnetic), N3 (diamagnetic) will:
A) attract N1 and N2 strongly but repel N3
B) attract N1 strongly, N2 weakly and repel N3 weakly
C) attract all three of them
D) attract N1 strongly, but repel N2 and N3 weakly
Answer: B) attract N1 strongly, N2 weakly and repel N3 weakly
Explanation: Ferromagnetics strongly attracted; paramagnetics weakly attracted; diamagnetics weakly repelled.