Magnetism
(a) Singly
(b) In pairs (north and south) ✅
(c) Random
(d) None
Explanation: Magnetic monopoles do not exist in nature; every magnet has both north and south poles.
Q2. Magnetic field lines are:
(a) Open lines
(b) Closed continuous loops ✅
(c) Random
(d) None
Explanation: They emerge from the north pole and enter the south pole, continuing inside the magnet.
Q3. Magnetic field is:
(a) Region where magnetic force acts ✅
(b) Region where electric force acts
(c) Random
(d) None
Explanation: It represents the influence of a magnet or current on other magnetic materials or charges.
Q4. Earth’s magnetism is due to:
(a) Currents in molten iron core ✅
(b) Charges at rest
(c) Random
(d) None
Explanation: The dynamo effect in Earth’s liquid outer core generates the geomagnetic field.
Q5. Magnetic declination is:
(a) Angle between geographic north and magnetic north ✅
(b) Angle between latitude and longitude
(c) Random
(d) None
Explanation: Declination varies with location and affects compass readings.
Q6. Magnetic inclination (dip) is:
(a) Angle between magnetic field and horizontal ✅
(b) Angle between magnetic field and vertical
(c) Random
(d) None
Explanation: Shows tilt of Earth’s magnetic field relative to the surface.
Q7. Magnetic moment is:
(a) Strength × length of magnet ✅
(b) Strength ÷ length
(c) Random
(d) None
Explanation: Vector quantity representing torque experienced by magnet in a field.
Q8. Torque on a bar magnet in uniform field is:
(a) Ï„ = MB sinθ ✅
(b) τ = MB cosθ
(c) Random
(d) None
Explanation: Torque depends on magnetic moment, field strength, and angle.
Q9. Magnetic materials are classified as:
(a) Diamagnetic, paramagnetic, ferromagnetic ✅
(b) Conductors, insulators
(c) Random
(d) None
Explanation: Classification based on response to external magnetic field.
Q10. Diamagnetic materials are:
(a) Weakly repelled by magnetic field ✅
(b) Strongly attracted
(c) Random
(d) None
Explanation: Examples include copper, bismuth; they have negative susceptibility.
Q11. Paramagnetic materials are:
(a) Weakly attracted by magnetic field ✅
(b) Strongly repelled
(c) Random
(d) None
Explanation: Examples include aluminum, platinum; they have small positive susceptibility.
Q12. Ferromagnetic materials are:
(a) Strongly attracted by magnetic field ✅
(b) Weakly repelled
(c) Random
(d) None
Explanation: Examples include iron, cobalt, nickel; they exhibit hysteresis.
Q13. Magnetic permeability is:
(a) Measure of ability to allow magnetic field ✅
(b) Measure of resistance
(c) Random
(d) None
Explanation: Higher permeability means stronger induced magnetic field.
Q14. Magnetic susceptibility is:
(a) Ratio of magnetization to applied field ✅
(b) Ratio of field to magnetization
(c) Random
(d) None
Explanation: Indicates how easily material can be magnetized.
Q15. Magnetic field due to straight current-carrying wire is:
(a) Circular around wire ✅
(b) Linear along wire
(c) Random
(d) None
Explanation: Direction given by right-hand thumb rule.
Q16. Biot–Savart law gives:
(a) Magnetic field due to current element ✅
(b) Electric field due to charge
(c) Random
(d) None
Explanation: dB ∝ Idl sinθ / r².
Q17. Ampere’s circuital law states:
(a) ∮B·dl = μ₀I ✅
(b) ∮E·dl = q/ε₀
(c) Random
(d) None
Explanation: Relates magnetic field around closed loop to current enclosed.
Q18. Magnetic field inside solenoid is:
(a) Uniform ✅
(b) Non-uniform
(c) Random
(d) None
Explanation: B = μ₀nI, strong and uniform inside solenoid.
Q19. Magnetic field inside toroid is:
(a) B = μ₀NI / 2Ï€r ✅
(b) B = μ₀nI
(c) Random
(d) None
Explanation: Depends on number of turns, current, and radius.
Q20. Lorentz force is:
(a) F = q(E + v × B) ✅
(b) F = qE
(c) Random
(d) None
Explanation: Force on moving charge in electric and magnetic fields.
Q21. Force on current-carrying conductor in magnetic field is:
(a) F = BIL sinθ ✅
(b) F = BIL cosθ
(c) Random
(d) None
Explanation: Basis of motor principle.
Q22. Right-hand thumb rule is used to:
(a) Find direction of magnetic field around conductor ✅
(b) Find direction of current
(c) Random
(d) None
Explanation: Thumb = current, curled fingers = field direction.
Q23. Fleming’s left-hand rule is used for:
(a) Motors ✅
(b) Generators
(c) Random
(d) None
Explanation: Thumb = force, forefinger = field, middle finger = current.
Q24. Fleming’s right-hand rule is used for:
(a) Generators ✅
(b) Motors
(c) Random
(d) None
Explanation: Thumb = motion, forefinger = field, middle finger = current.
Q25. Electromagnet is:
(a) Magnet produced by current ✅
(b) Natural magnet
(c) Random
(d) None
Explanation: Coil with current produces temporary magnetism, strength depends on turns and current.
Q26. Magnetic field due to circular loop at center is:
(a) B = μ₀I / 2R ✅
(b) B = μ₀I / R
(c) Random
(d) None
Explanation: Derived from Biot–Savart law, field is directly proportional to current and inversely proportional to radius.
Q27. Magnetic field due to long straight wire at distance r is:
(a) B = μ₀I / 2Ï€r ✅
(b) B = μ₀I / r
(c) Random
(d) None
Explanation: Field decreases with distance, direction given by right-hand rule.
Q28. Magnetic field inside solenoid is:
(a) B = μ₀nI ✅
(b) B = μ₀I / 2Ï€r
(c) Random
(d) None
Explanation: Uniform field inside solenoid, proportional to turns per unit length and current.
Q29. Magnetic field inside toroid is:
(a) B = μ₀NI / 2Ï€r ✅
(b) B = μ₀nI
(c) Random
(d) None
Explanation: Depends on number of turns, current, and radius of toroid.
Q30. Force on moving charge in magnetic field is:
(a) F = qvB sinθ ✅
(b) F = qvB cosθ
(c) Random
(d) None
Explanation: Maximum when velocity is perpendicular to field.
Q31. Direction of force on moving charge is given by:
(a) Right-hand rule ✅
(b) Left-hand rule
(c) Random
(d) None
Explanation: Thumb = velocity, fingers = field, palm = force direction.
Q32. Force on current-carrying conductor in magnetic field is:
(a) F = BIL sinθ ✅
(b) F = BIL cosθ
(c) Random
(d) None
Explanation: Basis of motor principle, force depends on length, current, and field.
Q33. Torque on current loop in magnetic field is:
(a) Ï„ = NIBA sinθ ✅
(b) τ = NIBA cosθ
(c) Random
(d) None
Explanation: Loop behaves like magnetic dipole, torque aligns it with field.
Q34. Magnetic dipole moment of current loop is:
(a) M = IA ✅
(b) M = I/A
(c) Random
(d) None
Explanation: Product of current and area vector.
Q35. Galvanometer works on:
(a) Deflection due to current in magnetic field ✅
(b) Heating effect
(c) Random
(d) None
Explanation: Measures small currents by coil deflection.
Q36. Ammeter is:
(a) Galvanometer with low resistance shunt ✅
(b) Galvanometer with high resistance
(c) Random
(d) None
Explanation: Measures current by allowing most current through shunt.
Q37. Voltmeter is:
(a) Galvanometer with high resistance series ✅
(b) Galvanometer with low resistance
(c) Random
(d) None
Explanation: Measures potential difference across points.
Q38. Electromagnet strength depends on:
(a) Number of turns and current ✅
(b) Voltage only
(c) Random
(d) None
Explanation: More turns and higher current produce stronger field.
Q39. Permanent magnet differs from electromagnet because:
(a) Retains magnetism without current ✅
(b) Needs current
(c) Random
(d) None
Explanation: Permanent magnets are naturally magnetized materials.
Q40. Magnetic shielding is done by:
(a) Using soft iron ✅
(b) Using copper
(c) Random
(d) None
Explanation: Soft iron redirects magnetic field lines, reducing field in protected region.
Q41. Magnetic hysteresis curve shows:
(a) Variation of B with H ✅
(b) Variation of E with H
(c) Random
(d) None
Explanation: Indicates lag of magnetization behind applied field.
Q42. Area of hysteresis loop represents:
(a) Energy loss per cycle ✅
(b) Magnetic strength
(c) Random
(d) None
Explanation: Energy dissipated as heat in magnetic material.
Q43. Soft magnetic materials are used in:
(a) Transformers ✅
(b) Permanent magnets
(c) Random
(d) None
Explanation: Low hysteresis loss, easy magnetization and demagnetization.
Q44. Hard magnetic materials are used in:
(a) Permanent magnets ✅
(b) Transformers
(c) Random
(d) None
Explanation: High coercivity, retain magnetism strongly.
Q45. Magnetic flux is:
(a) Φ = B·A cosθ ✅
(b) Φ = BA sinθ
(c) Random
(d) None
Explanation: Scalar quantity representing field lines through surface.
Q46. Unit of magnetic flux is:
(a) Weber ✅
(b) Tesla
(c) Random
(d) None
Explanation: 1 Wb = 1 T·m².
Q47. Unit of magnetic field is:
(a) Tesla ✅
(b) Weber
(c) Random
(d) None
Explanation: 1 T = 1 Wb/m².
Q48. Magnetic force between two parallel currents is:
(a) F/L = μ₀I₁I₂ / 2Ï€r ✅
(b) F/L = μ₀I₁I₂r
(c) Random
(d) None
Explanation: Basis of definition of ampere.
Q49. Two parallel currents in same direction:
(a) Attract each other ✅
(b) Repel each other
(c) Random
(d) None
Explanation: Magnetic fields interact to produce attraction.
Q50. Two parallel currents in opposite direction:
(a) Repel each other ✅
(b) Attract each other
(c) Random
(d) None
Explanation: Magnetic fields interact to produce repulsion.
Q51. Magnetic flux through a surface is:
(a) Φ = B·A cosθ ✅
(b) Φ = BA sinθ
(c) Random
(d) None
Explanation: Flux measures total magnetic field lines passing through a surface; depends on field strength, area, and orientation.
Q52. Unit of magnetic flux is:
(a) Weber ✅
(b) Tesla
(c) Random
(d) None
Explanation: 1 Wb = 1 T·m², representing field lines through 1 m² area with 1 Tesla field.
Q53. Magnetic flux density is:
(a) B = Φ/A ✅
(b) B = Φ × A
(c) Random
(d) None
Explanation: Field strength per unit area, measured in Tesla.
Q54. Magnetic induction is:
(a) Process of magnetizing material by external field ✅
(b) Process of demagnetizing
(c) Random
(d) None
Explanation: Causes alignment of domains in ferromagnetic materials.
Q55. Magnetic dipole in uniform field experiences:
(a) Torque but no net force ✅
(b) Force but no torque
(c) Random
(d) None
Explanation: Torque aligns dipole with field, but forces cancel out.
Q56. Magnetic dipole in non-uniform field experiences:
(a) Net force and torque ✅
(b) Only torque
(c) Random
(d) None
Explanation: Unequal forces on poles produce net force and torque.
Q57. Potential energy of magnetic dipole in field is:
(a) U = –MB cosθ ✅
(b) U = MB sinθ
(c) Random
(d) None
Explanation: Energy minimum when dipole aligns with field.
Q58. Magnetic field due to moving charge is given by:
(a) Biot–Savart law ✅
(b) Coulomb’s law
(c) Random
(d) None
Explanation: Relates current element to magnetic field produced.
Q59. Biot–Savart law formula is:
(a) dB = μ₀/4Ï€ × (Idl × r̂)/r² ✅
(b) dB = μ₀I/r
(c) Random
(d) None
Explanation: Vector law describing contribution of current element to field.
Q60. Ampere’s circuital law is useful for:
(a) Symmetric current distributions ✅
(b) Asymmetric distributions
(c) Random
(d) None
Explanation: Simplifies calculation of magnetic field in symmetric cases like solenoids, toroids.
Q61. Magnetic field inside infinite solenoid is:
(a) B = μ₀nI ✅
(b) B = μ₀I/2Ï€r
(c) Random
(d) None
Explanation: Uniform field, independent of position inside solenoid.
Q62. Magnetic field inside toroid depends on:
(a) Radius ✅
(b) Length
(c) Random
(d) None
Explanation: B = μ₀NI / 2Ï€r, inversely proportional to radius.
Q63. Magnetic field at center of circular coil is:
(a) B = μ₀NI / 2R ✅
(b) B = μ₀I/R
(c) Random
(d) None
Explanation: Depends on number of turns, current, and radius.
Q64. Magnetic field at axis of circular coil is:
(a) B = μ₀NI R² / 2(R² + x²)^(3/2) ✅
(b) B = μ₀NI / R
(c) Random
(d) None
Explanation: Derived from Biot–Savart law, decreases with distance x.
Q65. Magnetic dipole moment of coil is:
(a) M = NIA ✅
(b) M = I/A
(c) Random
(d) None
Explanation: Product of current, area, and number of turns.
Q66. Magnetic force on two parallel wires defines:
(a) Ampere ✅
(b) Coulomb
(c) Random
(d) None
Explanation: 1 Ampere is current producing 2×10⁻⁷ N/m force between wires 1 m apart.
Q67. Magnetic permeability of free space is:
(a) μ₀ = 4Ï€ × 10⁻⁷ H/m ✅
(b) μ₀ = 9 × 10⁹
(c) Random
(d) None
Explanation: Fundamental constant relating current to magnetic field.
Q68. Magnetic susceptibility of diamagnetic materials is:
(a) Negative ✅
(b) Positive
(c) Random
(d) None
Explanation: They oppose applied magnetic field.
Q69. Magnetic susceptibility of paramagnetic materials is:
(a) Small positive ✅
(b) Large positive
(c) Random
(d) None
Explanation: Weak attraction to magnetic field.
Q70. Magnetic susceptibility of ferromagnetic materials is:
(a) Very large positive ✅
(b) Negative
(c) Random
(d) None
Explanation: Strong attraction, domains align permanently.
Q71. Magnetic hysteresis is:
(a) Lag of magnetization behind applied field ✅
(b) Instantaneous response
(c) Random
(d) None
Explanation: Causes energy loss in magnetic cycles.
Q72. Area of hysteresis loop represents:
(a) Energy loss per cycle ✅
(b) Magnetic strength
(c) Random
(d) None
Explanation: Energy dissipated as heat in magnetic material.
Q73. Soft iron is used in transformers because:
(a) Low hysteresis loss ✅
(b) High coercivity
(c) Random
(d) None
Explanation: Easy magnetization and demagnetization reduces energy loss.
Q74. Steel is used for permanent magnets because:
(a) High coercivity ✅
(b) Low coercivity
(c) Random
(d) None
Explanation: Retains magnetism strongly due to domain structure.
Q75. Magnetic shielding is achieved by:
(a) Surrounding with soft iron ✅
(b) Surrounding with copper
(c) Random
(d) None
Explanation: Soft iron redirects magnetic field lines, reducing field inside shielded region.
Q76. Magnetic induction in ferromagnetic materials is due to:
(a) Alignment of domains ✅
(b) Free electrons
(c) Random
(d) None
Explanation: Domains are small regions with aligned magnetic moments; external field aligns them, producing strong magnetization.
Q77. Magnetic domains are:
(a) Regions with aligned atomic dipoles ✅
(b) Regions with random dipoles
(c) Random
(d) None
Explanation: In ferromagnets, domains align under external field, increasing magnetization.
Q78. Curie temperature is:
(a) Temperature above which ferromagnet loses magnetism ✅
(b) Temperature below which magnetism increases
(c) Random
(d) None
Explanation: Above Curie point, material becomes paramagnetic.
Q79. Magnetic hysteresis loop shows:
(a) Magnetization vs applied field ✅
(b) Voltage vs current
(c) Random
(d) None
Explanation: Indicates lag of magnetization behind external field, important in material selection.
Q80. Area of hysteresis loop represents:
(a) Energy loss per cycle ✅
(b) Magnetic strength
(c) Random
(d) None
Explanation: Energy dissipated as heat during magnetization cycles.
Q81. Soft magnetic materials are used in:
(a) Transformers ✅
(b) Permanent magnets
(c) Random
(d) None
Explanation: Low hysteresis loss, easy magnetization and demagnetization.
Q82. Hard magnetic materials are used in:
(a) Permanent magnets ✅
(b) Transformers
(c) Random
(d) None
Explanation: High coercivity, retain magnetism strongly.
Q83. Magnetic shielding is achieved by:
(a) Surrounding with soft iron ✅
(b) Surrounding with copper
(c) Random
(d) None
Explanation: Soft iron redirects magnetic field lines, reducing field inside shielded region.
Q84. Magnetic levitation works on:
(a) Repulsion between magnetic fields ✅
(b) Attraction only
(c) Random
(d) None
Explanation: Used in maglev trains, repulsive forces lift train above track.
Q85. MRI uses:
(a) Strong magnetic fields and radio waves ✅
(b) X-rays
(c) Random
(d) None
Explanation: Magnetic resonance imaging provides detailed body scans.
Q86. Magnetic energy stored in inductor is:
(a) U = ½ LI² ✅
(b) U = LI
(c) Random
(d) None
Explanation: Energy stored in magnetic field of inductor.
Q87. Magnetic flux linkage is:
(a) NΦ ✅
(b) Φ/N
(c) Random
(d) None
Explanation: Product of number of turns and flux through each turn.
Q88. Inductance depends on:
(a) Geometry and permeability ✅
(b) Voltage
(c) Random
(d) None
Explanation: Larger coil area, more turns, and higher permeability increase inductance.
Q89. Unit of inductance is:
(a) Henry ✅
(b) Tesla
(c) Random
(d) None
Explanation: 1 H = 1 Wb/A.
Q90. Self-induction is:
(a) Induced emf in coil due to change in its own current ✅
(b) Induced emf in another coil
(c) Random
(d) None
Explanation: Property of coil opposing change in current.
Q91. Mutual induction is:
(a) Induced emf in one coil due to change in current in another ✅
(b) Induced emf in same coil
(c) Random
(d) None
Explanation: Basis of transformer operation.
Q92. Transformer works on:
(a) Mutual induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Transfers AC voltage between coils via induction.
Q93. Step-up transformer increases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage greater than primary voltage.
Q94. Step-down transformer decreases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage less than primary voltage.
Q95. Generator works on:
(a) Electromagnetic induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Converts mechanical energy into electrical energy.
Q96. Motor works on:
(a) Force on current-carrying conductor in magnetic field ✅
(b) Electromagnetic induction
(c) Random
(d) None
Explanation: Converts electrical energy into mechanical energy.
Q97. Fleming’s left-hand rule is used for:
(a) Motors ✅
(b) Generators
(c) Random
(d) None
Explanation: Thumb = force, forefinger = field, middle finger = current.
Q98. Fleming’s right-hand rule is used for:
(a) Generators ✅
(b) Motors
(c) Random
(d) None
Explanation: Thumb = motion, forefinger = field, middle finger = current.
Q99. Magnetic braking works on:
(a) Eddy currents ✅
(b) Static friction
(c) Random
(d) None
Explanation: Eddy currents oppose motion, producing braking effect.
Q100. Eddy currents are:
(a) Currents induced in bulk conductor due to changing magnetic flux ✅
(b) Currents in insulators
(c) Random
(d) None
Explanation: Cause energy loss but useful in induction heating and braking.
Q101. Magnetic field due to infinite straight wire is:
(a) B = μ₀I / 2Ï€r ✅
(b) B = μ₀I / r
(c) Random
(d) None
Explanation: Field decreases inversely with distance, direction given by right-hand thumb rule.
Q102. Magnetic field at axis of circular coil is:
(a) B = μ₀NI R² / 2(R² + x²)^(3/2) ✅
(b) B = μ₀NI / R
(c) Random
(d) None
Explanation: Derived from Biot–Savart law, decreases with distance along axis.
Q103. Magnetic field inside long solenoid is:
(a) B = μ₀nI ✅
(b) B = μ₀I / 2Ï€r
(c) Random
(d) None
Explanation: Uniform field inside, proportional to turns per unit length and current.
Q104. Magnetic field inside toroid is:
(a) B = μ₀NI / 2Ï€r ✅
(b) B = μ₀nI
(c) Random
(d) None
Explanation: Depends on number of turns, current, and radius.
Q105. Magnetic dipole moment of current loop is:
(a) M = IA ✅
(b) M = I/A
(c) Random
(d) None
Explanation: Product of current and area vector.
Q106. Torque on current loop in magnetic field is:
(a) Ï„ = NIBA sinθ ✅
(b) τ = NIBA cosθ
(c) Random
(d) None
Explanation: Loop behaves like magnetic dipole, torque aligns it with field.
Q107. Potential energy of magnetic dipole in field is:
(a) U = –MB cosθ ✅
(b) U = MB sinθ
(c) Random
(d) None
Explanation: Energy minimum when dipole aligns with field.
Q108. Magnetic force on moving charge is:
(a) F = qvB sinθ ✅
(b) F = qvB cosθ
(c) Random
(d) None
Explanation: Maximum when velocity is perpendicular to field.
Q109. Direction of force on moving charge is given by:
(a) Right-hand rule ✅
(b) Left-hand rule
(c) Random
(d) None
Explanation: Thumb = velocity, fingers = field, palm = force.
Q110. Magnetic force on current-carrying conductor is:
(a) F = BIL sinθ ✅
(b) F = BIL cosθ
(c) Random
(d) None
Explanation: Basis of motor principle.
Q111. Magnetic force between two parallel currents is:
(a) F/L = μ₀I₁I₂ / 2Ï€r ✅
(b) F/L = μ₀I₁I₂r
(c) Random
(d) None
Explanation: Defines ampere, attraction if currents same direction.
Q112. Two parallel currents in same direction:
(a) Attract each other ✅
(b) Repel each other
(c) Random
(d) None
Explanation: Magnetic fields interact to produce attraction.
Q113. Two parallel currents in opposite direction:
(a) Repel each other ✅
(b) Attract each other
(c) Random
(d) None
Explanation: Magnetic fields interact to produce repulsion.
Q114. Magnetic flux linkage is:
(a) NΦ ✅
(b) Φ/N
(c) Random
(d) None
Explanation: Product of number of turns and flux through each turn.
Q115. Inductance of coil depends on:
(a) Geometry and permeability ✅
(b) Voltage
(c) Random
(d) None
Explanation: Larger coil area, more turns, and higher permeability increase inductance.
Q116. Unit of inductance is:
(a) Henry ✅
(b) Tesla
(c) Random
(d) None
Explanation: 1 H = 1 Wb/A.
Q117. Self-induction is:
(a) Induced emf in coil due to change in its own current ✅
(b) Induced emf in another coil
(c) Random
(d) None
Explanation: Property of coil opposing change in current.
Q118. Mutual induction is:
(a) Induced emf in one coil due to change in current in another ✅
(b) Induced emf in same coil
(c) Random
(d) None
Explanation: Basis of transformer operation.
Q119. Energy stored in inductor is:
(a) U = ½ LI² ✅
(b) U = LI
(c) Random
(d) None
Explanation: Energy stored in magnetic field of inductor.
Q120. Magnetic braking works on:
(a) Eddy currents ✅
(b) Static friction
(c) Random
(d) None
Explanation: Eddy currents oppose motion, producing braking effect.
Q121. Eddy currents are:
(a) Currents induced in bulk conductor due to changing magnetic flux ✅
(b) Currents in insulators
(c) Random
(d) None
Explanation: Cause energy loss but useful in induction heating and braking.
Q122. Eddy current loss is reduced by:
(a) Laminating core ✅
(b) Using solid core
(c) Random
(d) None
Explanation: Laminations reduce path for eddy currents, minimizing loss.
Q123. Transformer core is laminated to:
(a) Reduce eddy current loss ✅
(b) Increase resistance
(c) Random
(d) None
Explanation: Laminations minimize energy loss due to eddy currents.
Q124. Magnetic shielding is achieved by:
(a) Surrounding with soft iron ✅
(b) Surrounding with copper
(c) Random
(d) None
Explanation: Soft iron redirects magnetic field lines, reducing field inside shielded region.
Q125. Magnetic levitation works on:
(a) Repulsion between magnetic fields ✅
(b) Attraction only
(c) Random
(d) None
Explanation: Used in maglev trains, repulsive forces lift train above track.
Q126. Magnetic flux through a coil is:
(a) Φ = BA cosθ ✅
(b) Φ = BA sinθ
(c) Random
(d) None
Explanation: Flux depends on field strength, coil area, and orientation relative to field.
Q127. Faraday’s law of electromagnetic induction states:
(a) Induced emf ∝ rate of change of flux ✅
(b) Induced emf ∝ flux
(c) Random
(d) None
Explanation: emf = –dΦ/dt, negative sign indicates Lenz’s law.
Q128. Lenz’s law states:
(a) Induced current opposes change in flux ✅
(b) Induced current aids change
(c) Random
(d) None
Explanation: Ensures conservation of energy in induction.
Q129. Induced emf in coil is:
(a) e = –N dΦ/dt ✅
(b) e = NΦ
(c) Random
(d) None
Explanation: emf proportional to number of turns and rate of flux change.
Q130. Self-inductance is:
(a) emf induced in coil due to change in its own current ✅
(b) emf induced in another coil
(c) Random
(d) None
Explanation: Property of coil opposing change in current.
Q131. Mutual inductance is:
(a) emf induced in one coil due to change in current in another ✅
(b) emf induced in same coil
(c) Random
(d) None
Explanation: Basis of transformer operation.
Q132. Unit of inductance is:
(a) Henry ✅
(b) Tesla
(c) Random
(d) None
Explanation: 1 H = 1 Wb/A.
Q133. Energy stored in inductor is:
(a) U = ½ LI² ✅
(b) U = LI
(c) Random
(d) None
Explanation: Energy stored in magnetic field of coil.
Q134. Induced emf in moving conductor is:
(a) e = Blv sinθ ✅
(b) e = Blv cosθ
(c) Random
(d) None
Explanation: Motional emf depends on length, velocity, and field strength.
Q135. Fleming’s right-hand rule is used for:
(a) Generators ✅
(b) Motors
(c) Random
(d) None
Explanation: Thumb = motion, forefinger = field, middle finger = current.
Q136. Fleming’s left-hand rule is used for:
(a) Motors ✅
(b) Generators
(c) Random
(d) None
Explanation: Thumb = force, forefinger = field, middle finger = current.
Q137. Transformer works on:
(a) Mutual induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Transfers AC voltage between coils via induction.
Q138. Step-up transformer increases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage greater than primary voltage.
Q139. Step-down transformer decreases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage less than primary voltage.
Q140. Efficiency of transformer is:
(a) η = (Output power / Input power) × 100% ✅
(b) η = Output/Input
(c) Random
(d) None
Explanation: Efficiency close to 95–99% in practical transformers.
Q141. Eddy currents are:
(a) Currents induced in bulk conductor due to changing flux ✅
(b) Currents in insulators
(c) Random
(d) None
Explanation: Cause energy loss but useful in induction heating and braking.
Q142. Eddy current loss is reduced by:
(a) Laminating core ✅
(b) Using solid core
(c) Random
(d) None
Explanation: Laminations minimize path for eddy currents.
Q143. Magnetic braking works on:
(a) Eddy currents ✅
(b) Static friction
(c) Random
(d) None
Explanation: Eddy currents oppose motion, producing braking effect.
Q144. Induction heating works on:
(a) Eddy currents ✅
(b) Static friction
(c) Random
(d) None
Explanation: Eddy currents produce heat in conductor.
Q145. Generator works on:
(a) Electromagnetic induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Converts mechanical energy into electrical energy.
Q146. Motor works on:
(a) Force on conductor in magnetic field ✅
(b) Electromagnetic induction
(c) Random
(d) None
Explanation: Converts electrical energy into mechanical energy.
Q147. Alternating current is generated by:
(a) Rotating coil in magnetic field ✅
(b) Static coil
(c) Random
(d) None
Explanation: Rotation changes flux, inducing alternating emf.
Q148. DC generator uses:
(a) Commutator ✅
(b) Slip rings
(c) Random
(d) None
Explanation: Commutator converts alternating emf into direct current.
Q149. AC generator uses:
(a) Slip rings ✅
(b) Commutator
(c) Random
(d) None
Explanation: Slip rings maintain alternating emf output.
Q150. Magnetic flux in generator coil changes due to:
(a) Rotation of coil ✅
(b) Static coil
(c) Random
(d) None
Explanation: Rotating coil changes angle with field, producing alternating flux.
Q151. Magnetic flux through a surface depends on:
(a) Field strength, area, orientation ✅
(b) Only area
(c) Random
(d) None
Explanation: Flux = B·A cosθ, maximum when field is perpendicular to surface.
Q152. Faraday’s law states:
(a) Induced emf ∝ rate of change of flux ✅
(b) Induced emf ∝ flux
(c) Random
(d) None
Explanation: emf = –dΦ/dt, negative sign indicates opposition to change.
Q153. Lenz’s law ensures:
(a) Conservation of energy ✅
(b) Conservation of charge
(c) Random
(d) None
Explanation: Induced current opposes change in flux, preventing perpetual motion.
Q154. Induced emf in rotating coil is:
(a) e = NBAω sinωt ✅
(b) e = NBAω cosωt
(c) Random
(d) None
Explanation: Alternating emf generated in AC generator.
Q155. Average emf induced in coil is:
(a) e = –ΔΦ/Δt ✅
(b) e = Φ/t
(c) Random
(d) None
Explanation: Depends on change in flux over time interval.
Q156. Motional emf is:
(a) e = Blv sinθ ✅
(b) e = Blv cosθ
(c) Random
(d) None
Explanation: emf induced when conductor moves in magnetic field.
Q157. Induced current direction is given by:
(a) Lenz’s law ✅
(b) Ohm’s law
(c) Random
(d) None
Explanation: Current always opposes change in flux.
Q158. Self-inductance opposes:
(a) Change in current ✅
(b) Change in voltage
(c) Random
(d) None
Explanation: Coil resists variation in current by inducing emf.
Q159. Mutual inductance depends on:
(a) Geometry and relative position of coils ✅
(b) Voltage
(c) Random
(d) None
Explanation: Greater coupling increases mutual inductance.
Q160. Transformer efficiency is high because:
(a) Uses laminated core ✅
(b) Uses solid core
(c) Random
(d) None
Explanation: Laminations reduce eddy current loss, improving efficiency.
Q161. Eddy currents are reduced by:
(a) Laminating core ✅
(b) Using thick solid core
(c) Random
(d) None
Explanation: Laminations restrict current paths, minimizing losses.
Q162. Induction heating is used in:
(a) Cooking and metallurgy ✅
(b) Cooling
(c) Random
(d) None
Explanation: Eddy currents produce heat in conductor, useful in industry.
Q163. Magnetic braking is used in:
(a) Trains and amusement rides ✅
(b) Electric circuits
(c) Random
(d) None
Explanation: Eddy currents oppose motion, slowing down moving parts.
Q164. AC generator produces:
(a) Alternating current ✅
(b) Direct current
(c) Random
(d) None
Explanation: Rotating coil in magnetic field induces alternating emf.
Q165. DC generator uses:
(a) Commutator ✅
(b) Slip rings
(c) Random
(d) None
Explanation: Commutator converts alternating emf into direct current.
Q166. AC generator uses:
(a) Slip rings ✅
(b) Commutator
(c) Random
(d) None
Explanation: Slip rings maintain alternating emf output.
Q167. Motor principle is:
(a) Force on current-carrying conductor in magnetic field ✅
(b) Induction of emf
(c) Random
(d) None
Explanation: Converts electrical energy into mechanical energy.
Q168. Generator principle is:
(a) Electromagnetic induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Converts mechanical energy into electrical energy.
Q169. Alternating emf in generator coil is:
(a) e = NBAω sinωt ✅
(b) e = NBAω cosωt
(c) Random
(d) None
Explanation: emf varies sinusoidally with time.
Q170. Transformer works only with:
(a) Alternating current ✅
(b) Direct current
(c) Random
(d) None
Explanation: Requires changing flux to induce emf in secondary coil.
Q171. Step-up transformer increases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage greater than primary voltage.
Q172. Step-down transformer decreases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage less than primary voltage.
Q173. Efficiency of transformer is:
(a) η = (Output power / Input power) × 100% ✅
(b) η = Output/Input
(c) Random
(d) None
Explanation: Practical transformers achieve 95–99% efficiency.
Q174. Magnetic flux in generator coil changes due to:
(a) Rotation of coil ✅
(b) Static coil
(c) Random
(d) None
Explanation: Rotation changes angle with field, producing alternating flux.
Q175. Alternating current frequency depends on:
(a) Speed of rotation ✅
(b) Voltage
(c) Random
(d) None
Explanation: Higher rotation speed increases frequency of AC output.
Q176. Magnetic flux linkage in coil is:
(a) NΦ ✅
(b) Φ/N
(c) Random
(d) None
Explanation: Total flux linked with coil equals flux per turn multiplied by number of turns.
Q177. Induced emf in coil rotating in uniform field is:
(a) e = NBAω sinωt ✅
(b) e = NBAω cosωt
(c) Random
(d) None
Explanation: emf varies sinusoidally with time, basis of AC generation.
Q178. Average emf induced in coil is:
(a) e = –ΔΦ/Δt ✅
(b) e = Φ/t
(c) Random
(d) None
Explanation: emf depends on rate of change of flux over time interval.
Q179. Lenz’s law direction of induced current:
(a) Opposes change in flux ✅
(b) Aids change
(c) Random
(d) None
Explanation: Ensures conservation of energy, prevents perpetual motion.
Q180. Self-inductance opposes:
(a) Change in current ✅
(b) Change in voltage
(c) Random
(d) None
Explanation: Coil resists variation in current by inducing emf.
Q181. Mutual inductance is maximum when:
(a) Coils are closely coupled ✅
(b) Coils are far apart
(c) Random
(d) None
Explanation: Greater coupling increases mutual inductance.
Q182. Transformer works on:
(a) Mutual induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Transfers AC voltage between coils via induction.
Q183. Step-up transformer increases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage greater than primary voltage.
Q184. Step-down transformer decreases:
(a) Voltage ✅
(b) Current
(c) Random
(d) None
Explanation: Secondary voltage less than primary voltage.
Q185. Efficiency of transformer is:
(a) η = (Output power / Input power) × 100% ✅
(b) η = Output/Input
(c) Random
(d) None
Explanation: Practical transformers achieve 95–99% efficiency.
Q186. Eddy currents are:
(a) Currents induced in bulk conductor due to changing flux ✅
(b) Currents in insulators
(c) Random
(d) None
Explanation: Cause energy loss but useful in induction heating and braking.
Q187. Eddy current loss is reduced by:
(a) Laminating core ✅
(b) Using solid core
(c) Random
(d) None
Explanation: Laminations restrict current paths, minimizing losses.
Q188. Induction heating works on:
(a) Eddy currents ✅
(b) Static friction
(c) Random
(d) None
Explanation: Eddy currents produce heat in conductor, useful in cooking and metallurgy.
Q189. Magnetic braking is used in:
(a) Trains and amusement rides ✅
(b) Electric circuits
(c) Random
(d) None
Explanation: Eddy currents oppose motion, slowing down moving parts.
Q190. AC generator principle is:
(a) Electromagnetic induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Converts mechanical energy into electrical energy.
Q191. DC generator uses:
(a) Commutator ✅
(b) Slip rings
(c) Random
(d) None
Explanation: Commutator converts alternating emf into direct current.
Q192. AC generator uses:
(a) Slip rings ✅
(b) Commutator
(c) Random
(d) None
Explanation: Slip rings maintain alternating emf output.
Q193. Alternating emf in generator coil is:
(a) e = NBAω sinωt ✅
(b) e = NBAω cosωt
(c) Random
(d) None
Explanation: emf varies sinusoidally with time.
Q194. Frequency of AC depends on:
(a) Speed of rotation ✅
(b) Voltage
(c) Random
(d) None
Explanation: Higher rotation speed increases frequency of AC output.
Q195. Motor principle is:
(a) Force on current-carrying conductor in magnetic field ✅
(b) Induction of emf
(c) Random
(d) None
Explanation: Converts electrical energy into mechanical energy.
Q196. Generator principle is:
(a) Electromagnetic induction ✅
(b) Electrostatics
(c) Random
(d) None
Explanation: Converts mechanical energy into electrical energy.
Q197. Alternating current is generated by:
(a) Rotating coil in magnetic field ✅
(b) Static coil
(c) Random
(d) None
Explanation: Rotation changes flux, inducing alternating emf.
Q198. Magnetic flux in generator coil changes due to:
(a) Rotation of coil ✅
(b) Static coil
(c) Random
(d) None
Explanation: Rotation changes angle with field, producing alternating flux.
Q199. Transformer works only with:
(a) Alternating current ✅
(b) Direct current
(c) Random
(d) None
Explanation: Requires changing flux to induce emf in secondary coil.
Q200. Magnetic applications overall include:
(a) Motors, generators, transformers, MRI, maglev ✅
(b) Cooking only
(c) Random
(d) None
Explanation: Magnetism underpins modern technology from power generation to medical imaging.
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