Magnetic Effects of Electric Current Part 3: MCQs (Q51–Q75)
🧲 Magnetic Effects of Electric Current – MCQs (Class 10 Science, NCERT)
🔹 Part 3: Questions 51–75
Q51. In domestic electric circuits, the live wire is usually of which colour?
A) Black
B) Green
C) Red
D) Blue
Correct Answer: C) Red
Explanation:
- ✅ C) Red → Live wire.
- A) Black → Neutral wire.
- B) Green → Earth wire.
- D) Blue → May also denote neutral (alternate coding).
Q52. In India, the neutral wire is usually of which colour?
A) Blue/Black
B) Green
C) Red
D) Yellow
Correct Answer: A) Blue/Black
Explanation:
- ✅ A) Neutral wire is coded blue (sometimes black).
Q53. In household wiring, the fuse is connected in which wire?
A) Live wire
B) Neutral wire
C) Earth wire
D) Both live and neutral
Correct Answer: A) Live wire
Explanation:
- ✅ A) Fuse cuts off supply if current exceeds safe limit.
Q54. The function of earth wire in domestic circuits is to:
A) Prevent short-circuit
B) Prevent overload
C) Avoid electric shock
D) Reduce power loss
Correct Answer: C) Avoid electric shock
Explanation:
- ✅ C) Earth wire directs leakage current safely into the ground.
Q55. The function of commutator in a motor is to:
A) Change current into AC
B) Change direction of current every half rotation
C) Provide energy
D) Increase resistance
Correct Answer: B) Change direction of current every half rotation
Explanation:
- ✅ B) Ensures continuous unidirectional torque.
Q56. The device which produces induced current is:
A) Motor
B) Generator
C) Battery
D) Transformer
Correct Answer: B) Generator
Explanation:
- ✅ B) Generator → Electromagnetic induction principle.
Q57. The magnetic effect of current was discovered by:
A) Faraday
B) Oersted
C) Ampere
D) Fleming
Correct Answer: B) Oersted
Explanation:
- ✅ B) Oersted discovered deflection of compass needle near current.
Q58. Electromagnetic induction was discovered by:
A) Oersted
B) Faraday
C) Ampere
D) Fleming
Correct Answer: B) Faraday
Explanation:
- ✅ B) Faraday → Changing flux induces current.
Q59. The magnitude of induced current depends on:
A) Rate of change of magnetic flux
B) Resistance of coil
C) Strength of magnet
D) All of these
Correct Answer: D) All of these
Explanation:
- ✅ D) All factors affect induced current (Faraday’s law + Ohm’s law).
Q60. The direction of induced current is given by:
A) Fleming’s left-hand rule
B) Fleming’s right-hand rule
C) Lenz’s law
D) Ampere’s law
Correct Answer: B) Fleming’s right-hand rule
Explanation:
- ✅ B) Right-hand rule: Thumb = motion, First finger = field, Second = current.
Q61. The alternating current reverses direction after every:
A) 1 second
B) 1/50 second
C) 1/100 second
D) 1/25 second
Correct Answer: B) 1/50 second
Explanation:
- ✅ B) In India, f = 50 Hz → Time period T = 1/f = 1/50 s.
Q62. The main advantage of AC over DC is:
A) Can be transmitted easily over long distances
B) Safer
C) Cheaper appliances
D) Constant direction
Correct Answer: A) Can be transmitted easily over long distances
Explanation:
- ✅ A) AC voltage can be stepped up or down with transformers.
Q63. The frequency of DC is:
A) 50 Hz
B) 60 Hz
C) Zero
D) Infinity
Correct Answer: C) Zero
Explanation:
- ✅ C) DC has constant value → no frequency.
Q64. Which of the following uses electromagnets?
A) Electric bell
B) Electric motor
C) Loudspeaker
D) All of these
Correct Answer: D) All of these
Explanation:
- ✅ D) All devices depend on electromagnets.
Q65. The north pole of a freely suspended bar magnet points towards:
A) Geographic north
B) Geographic south
C) Magnetic south
D) Magnetic centre
Correct Answer: A) Geographic north
Explanation:
- ✅ A) Actually attracted to Earth’s magnetic south, located near geographic north.
Q66. Which is true about magnetic field lines?
A) They cross each other
B) They always form closed loops
C) They start and end at same pole
D) They are straight
Correct Answer: B) They always form closed loops
Explanation:
- ✅ B) Outside magnet: N → S; Inside magnet: S → N.
Q67. The Earth’s magnetic field protects us from:
A) UV rays
B) Cosmic rays
C) Sound waves
D) Infrared rays
Correct Answer: B) Cosmic rays
Explanation:
- ✅ B) Earth’s field deflects harmful charged cosmic particles.
Q68. The magnetic field strength around a wire is directly proportional to:
A) Voltage
B) Resistance
C) Current
D) Length
Correct Answer: C) Current
Explanation:
- ✅ C) B ∝ I.
Q69. Which one is not a safety measure in household electric circuit?
A) Earthing
B) Fuse
C) MCB
D) Overloading
Correct Answer: D) Overloading
Explanation:
- ✅ D) Overloading is unsafe, others are safety measures.
Q70. The field lines around a bar magnet are densest at:
A) Centre
B) Poles
C) Equator
D) Midpoint
Correct Answer: B) Poles
Explanation:
- ✅ B) Strongest field at poles.
Q71. Which of the following is not an application of electromagnetic induction?
A) Generator
B) Transformer
C) Electric motor
D) Induction cooker
Correct Answer: C) Electric motor
Explanation:
- ✅ C) Motor works on magnetic effect of current, not induction.
Q72. The unit of magnetic flux is:
A) Weber
B) Tesla
C) Newton
D) Ampere
Correct Answer: A) Weber
Explanation:
- ✅ A) Flux = B × A, unit = Weber.
Q73. The unit of magnetic flux density is:
A) Weber
B) Tesla
C) Ampere
D) Henry
Correct Answer: B) Tesla
Explanation:
- ✅ B) B = Φ/A, unit Tesla = Wb/m².
Q74. In an electric generator, current in coil is induced because of:
A) Heating effect
B) Chemical reaction
C) Rotating coil in magnetic field
D) Battery supply
Correct Answer: C) Rotating coil in magnetic field
Explanation:
- ✅ C) Rotation → Changing flux → Induced current.
Q75. The device that prevents damage to appliances during power surges is:
A) Fuse
B) Switch
C) Battery
D) Socket
Correct Answer: A) Fuse
Explanation:
- ✅ A) Fuse melts if current exceeds safe value.
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