🧲 Magnetic Effects of Electric Current – MCQs (Class 10 Science, NCERT)

🔹 Part 4: Questions 76–100

Q76. The phenomenon of production of current in a conductor by changing magnetic field around it is called:

A) Magnetic effect of current
B) Heating effect of current
C) Electromagnetic induction
D) Electric discharge

Correct Answer: C) Electromagnetic induction

Explanation:

• ✅ C) Faraday’s law → Current induced by changing magnetic flux.

Q77. The function of carbon brushes in motor or generator is:

A) Increase speed
B) Reverse current
C) Provide connection between coil and external circuit
D) Decrease resistance

Correct Answer: C) Provide connection between coil and external circuit

Explanation:

• ✅ C) Brushes maintain contact with commutator/slip rings.

Q78. Which device works on Fleming’s left-hand rule?

A) Generator
B) Motor
C) Transformer
D) Fuse

Correct Answer: B) Motor

Explanation:

• ✅ B) Motor: Force direction determined by left-hand rule.

Q79. Which device works on Fleming’s right-hand rule?

A) Motor
B) Generator
C) Transformer
D) Battery

Correct Answer: B) Generator

Explanation:

• ✅ B) Right-hand rule → Direction of induced current in generator.

Q80. In an AC generator, commutator is replaced by:

A) Slip rings
B) Brushes
C) Coil
D) Magnet

Correct Answer: A) Slip rings

Explanation:

• ✅ A) Slip rings allow output of alternating current.

Q81. The core of electromagnet is made of:

A) Copper
B) Soft iron
C) Steel
D) Aluminium

Correct Answer: B) Soft iron

Explanation:

• ✅ B) Soft iron magnetises & demagnetises easily.

Q82. Which type of current is used in household supply in India?

A) AC of 220 V, 50 Hz
B) DC of 220 V
C) AC of 110 V, 60 Hz
D) DC of 440 V

Correct Answer: A) AC of 220 V, 50 Hz

Explanation:

• ✅ A) Standard supply in India.

Q83. The advantage of AC over DC is:

A) AC cannot be transmitted
B) AC can be stepped up/down by transformer
C) AC is constant
D) DC is cheaper

Correct Answer: B) AC can be stepped up/down by transformer

Explanation:

• ✅ B) Step-up → less loss in transmission.

Q84. An electric motor converts:

A) Electrical → Mechanical energy
B) Mechanical → Electrical energy
C) Electrical → Heat energy
D) Mechanical → Heat energy

Correct Answer: A) Electrical → Mechanical energy

Explanation:

• ✅ A) Motor principle.

Q85. An electric generator converts:

A) Electrical → Mechanical energy
B) Mechanical → Electrical energy
C) Heat → Electrical energy
D) Chemical → Electrical energy

Correct Answer: B) Mechanical → Electrical energy

Explanation:

• ✅ B) Generator principle.

Q86. The direction of magnetic field lines inside a bar magnet is:

A) South to North
B) North to South
C) Random
D) Circular

Correct Answer: A) South to North

Explanation:

• ✅ A) Inside → S → N; Outside → N → S.

Q87. Which rule helps to find the direction of magnetic field around a conductor?

A) Fleming’s rule
B) Right-hand thumb rule
C) Lenz’s law
D) Ampere’s law

Correct Answer: B) Right-hand thumb rule

Explanation:

• ✅ B) Thumb = current, curled fingers = field direction.

Q88. Which device prevents electric shock due to leakage currents?

A) Fuse
B) Earthing
C) Switch
D) Battery

Correct Answer: B) Earthing

Explanation:

• ✅ B) Earth wire transfers leakage current safely to ground.

Q89. When the current in a conductor is doubled, the magnetic field produced:

A) Remains same
B) Doubles
C) Becomes half
D) Becomes four times

Correct Answer: B) Doubles

Explanation:

• ✅ B) B ∝ I.

Q90. The strength of magnetic field is indicated by:

A) Number of lines of force
B) Length of conductor
C) Voltage
D) Current only

Correct Answer: A) Number of lines of force

Explanation:

• ✅ A) More lines/closer spacing → Stronger field.

Q91. In a DC motor, split rings are used instead of slip rings because:

A) To maintain AC
B) To maintain unidirectional torque
C) To reduce heating
D) To avoid sparks

Correct Answer: B) To maintain unidirectional torque

Explanation:

• ✅ B) Split rings reverse current → Continuous rotation.

Q92. The Earth’s magnetic field is due to:

A) Mountains
B) Electric currents in molten core
C) Sunlight
D) Gravity

Correct Answer: B) Electric currents in molten core

Explanation:

• ✅ B) Earth behaves like giant bar magnet.

Q93. A magnetic compass is deflected near a current-carrying wire because:

A) Wire becomes magnetised
B) Current produces magnetic field
C) Wire attracts compass
D) Wire repels compass

Correct Answer: B) Current produces magnetic field

Explanation:

• ✅ B) Oersted’s experiment.

Q94. Magnetic field strength at centre of a circular coil increases when:

A) Current decreases
B) Radius increases
C) Number of turns increases
D) Wire length decreases

Correct Answer: C) Number of turns increases

Explanation:

• ✅ C) B ∝ N (number of turns).

Q95. A straight conductor carrying current produces magnetic field in which direction?

A) Along current
B) Perpendicular circular around conductor
C) Parallel to wire
D) Random

Correct Answer: B) Perpendicular circular around conductor

Explanation:

• ✅ B) Field forms concentric circles.

Q96. Which factor does NOT affect force on a current-carrying conductor in magnetic field?

A) Current in conductor
B) Length of conductor
C) Strength of magnetic field
D) Mass of conductor

Correct Answer: D) Mass of conductor

Explanation:

• ✅ D) F = BIL sinθ (mass irrelevant).

Q97. The direction of force on a current-carrying conductor in a magnetic field is given by:

A) Fleming’s left-hand rule
B) Fleming’s right-hand rule
C) Ampere’s law
D) Right-hand thumb rule

Correct Answer: A) Fleming’s left-hand rule

Explanation:

• ✅ A) Thumb = force, First finger = field, Second = current.

Q98. The working principle of loudspeaker is:

A) Heating effect of current
B) Magnetic effect of current
C) Electromagnetic induction
D) Chemical effect of current

Correct Answer: B) Magnetic effect of current

Explanation:

• ✅ B) Coil + magnet → Vibrations produce sound.

Q99. A device used to convert AC to DC is:

A) Transformer
B) Rectifier
C) Motor
D) Generator

Correct Answer: B) Rectifier

Explanation:

• ✅ B) Rectifier uses diodes.

Q100. Which of the following is NOT true about magnetic field lines?

A) They never intersect
B) They form closed loops
C) They originate from south pole outside magnet
D) Denser lines indicate stronger field

Correct Answer: C) They originate from south pole outside magnet

Explanation:

• ✅ C) Field originates from North → South outside magnet.

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