Class 10 Science NCERT MCQs Chapter 12 Magnetic Effects of Electric Current

 


NCERT MCQs of Class 10 Science, Chapter 12, Magnetic Effects of Electric Current

  • 1) A magnetic field is produced around a current-carrying conductor due to:
    a) Electrostatic force
    b) Motion of electrons
    c) Gravitational force
    d) Nuclear force
    Answer: b) Motion of electrons
    Explanation: The movement of electrons (electric current) in a conductor generates a magnetic field around it.

  • 2) The direction of the magnetic field around a straight current-carrying conductor can be determined using:
    a) Fleming’s Left-Hand Rule
    b) Fleming’s Right-Hand Rule
    c) Right-Hand Thumb Rule
    d) Left-Hand Thumb Rule
    Answer: c) Right-Hand Thumb Rule
    Explanation: According to the Right-Hand Thumb Rule, if the thumb points in the direction of current, the fingers curl in the direction of the magnetic field.

  • 3) The field lines around a current-carrying straight conductor are:
    a) Straight lines
    b) Concentric circles
    c) Radial lines
    d) Parallel lines
    Answer: b) Concentric circles
    Explanation: The magnetic field around a straight conductor forms concentric circles centered around the conductor.

  • 4) The strength of a magnetic field produced by a current-carrying conductor increases with:
    a) Decreasing current
    b) Increasing distance from the conductor
    c) Increasing current
    d) Both a and b
    Answer: c) Increasing current
    Explanation: A stronger current produces a stronger magnetic field.

  • 5) Which device is used to show the presence of a magnetic field?
    a) Voltmeter
    b) Ammeter
    c) Magnetic compass
    d) Galvanometer
    Answer: c) Magnetic compass
    Explanation: A magnetic compass aligns with the field and shows the presence of a magnetic field.

  • 6) What happens to a current-carrying conductor placed in a magnetic field?
    a) It experiences a force
    b) It gets heated
    c) It stops conducting electricity
    d) Nothing happens
    Answer: a) It experiences a force
    Explanation: According to Fleming’s Left-Hand Rule, a conductor placed in a magnetic field experiences a force.

  • 7) Which rule is used to determine the direction of force on a current-carrying conductor in a magnetic field?
    a) Right-Hand Thumb Rule
    b) Fleming’s Left-Hand Rule
    c) Fleming’s Right-Hand Rule
    d) Ampere’s Rule
    Answer: b) Fleming’s Left-Hand Rule
    Explanation: Fleming’s Left-Hand Rule helps find the direction of force in a motor.

  • 8) A current-carrying coil behaves like a magnet because of:
    a) Electrostatic force
    b) Moving charges
    c) Gravitational force
    d) Sound energy
    Answer: b) Moving charges
    Explanation: The movement of charges in a coil produces a magnetic field, making it behave like a magnet.

  • 9) What is the shape of the magnetic field around a solenoid?
    a) Circular
    b) Straight lines
    c) Similar to a bar magnet
    d) Random
    Answer: c) Similar to a bar magnet
    Explanation: A solenoid produces a magnetic field similar to a bar magnet, with north and south poles.

  • 10) The device that converts electrical energy into mechanical energy is:
    a) Electric generator
    b) Transformer
    c) Electric motor
    d) Voltmeter
    Answer: c) Electric motor
    Explanation: An electric motor converts electrical energy into mechanical energy.

  • 11) Which of the following parts is NOT present in an electric motor?
    a) Armature
    b) Brushes
    c) Slip rings
    d) Commutator
    Answer: c) Slip rings
    Explanation: Slip rings are used in AC generators, while commutators are used in DC motors.

  • 12) A coil of wire carrying current produces:
    a) Heat only
    b) Only electric field
    c) Magnetic field only
    d) Both electric and magnetic fields
    Answer: d) Both electric and magnetic fields
    Explanation: A current-carrying coil generates both an electric and magnetic field.

  • 13) Which device converts mechanical energy into electrical energy?
    a) Electric motor
    b) Electric generator
    c) Transformer
    d) Ammeter
    Answer: b) Electric generator
    Explanation: An electric generator converts mechanical energy into electrical energy.

  • 14) Which rule is used to determine the direction of induced current in a generator?
    a) Fleming’s Left-Hand Rule
    b) Fleming’s Right-Hand Rule
    c) Right-Hand Thumb Rule
    d) Ampere’s Rule
    Answer: b) Fleming’s Right-Hand Rule
    Explanation: Fleming’s Right-Hand Rule is used to find the direction of induced current in a generator.

  • 15) What is electromagnetic induction?
    a) Generating electric current using heat
    b) Inducing voltage in a coil due to a changing magnetic field
    c) Converting electrical energy into mechanical energy
    d) Producing electricity using chemical reactions
    Answer: b) Inducing voltage in a coil due to a changing magnetic field
    Explanation: Electromagnetic induction occurs when a changing magnetic field induces voltage in a conductor.

  • 16) Which device works on the principle of electromagnetic induction?
    a) Electric motor
    b) Transformer
    c) Battery
    d) Solar panel
    Answer: b) Transformer
    Explanation: A transformer works on electromagnetic induction to change voltage levels.

  • 17) Which of the following statements is correct for a bar magnet?
    a) Like poles attract each other
    b) Unlike poles repel each other
    c) Magnetic field lines start from the north pole and end at the south pole
    d) Magnetic field lines form closed loops inside the magnet
    Answer: c) Magnetic field lines start from the north pole and end at the south pole
    Explanation: Magnetic field lines originate from the north pole and terminate at the south pole.

  • 18) What is the function of a split-ring commutator in a DC motor?
    a) To increase voltage
    b) To reverse current direction
    c) To decrease resistance
    d) To store energy
    Answer: b) To reverse current direction
    Explanation: A split-ring commutator ensures continuous rotation by reversing current direction in a DC motor.

  • 19) Why does a freely suspended magnet always point in the north-south direction?
    a) Due to Earth’s gravitational force
    b) Due to Earth's magnetic field
    c) Due to electrostatic force
    d) Due to its weight
    Answer: b) Due to Earth's magnetic field
    Explanation: A freely suspended magnet aligns itself with Earth’s magnetic field.

  • 20) The core of an electromagnet is usually made of:
    a) Copper
    b) Steel
    c) Soft iron
    d) Aluminum
    Answer: c) Soft iron
    Explanation: Soft iron is used as the core in electromagnets because it increases magnetic strength and loses magnetism quickly when current is switched off.

  • 21) Which of the following statements is true about magnetic field lines?
    a) They always cross each other.
    b) They originate from the south pole and end at the north pole.
    c) They form closed loops.
    d) They are straight lines.
    Answer: c) They form closed loops.
    Explanation: Magnetic field lines start from the north pole and end at the south pole outside the magnet, but inside the magnet, they travel from south to north, forming closed loops.

  • 22) The force experienced by a current-carrying conductor in a magnetic field depends on:
    a) The magnitude of the current
    b) The strength of the magnetic field
    c) The angle between the current and the magnetic field
    d) All of the above
    Answer: d) All of the above
    Explanation: The force (FFF) on a current-carrying conductor in a magnetic field is given by F=BILsin⁡θF = BIL \sin \thetaF=BILsinθ, where B = magnetic field, I = current, L = length of conductor, and θ\thetaθ = angle between current and field.

  • 23) An electric current can produce:
    a) Only heat
    b) Only a magnetic field
    c) Heat and magnetic field
    d) Sound energy
    Answer: c) Heat and magnetic field
    Explanation: A current-carrying conductor produces both heat (Joule heating) and a magnetic field.

  • 24) If the current in a solenoid is increased, what happens to the strength of its magnetic field?
    a) Increases
    b) Decreases
    c) Remains unchanged
    d) Becomes zero
    Answer: a) Increases
    Explanation: The magnetic field strength of a solenoid is directly proportional to the current passing through it.

  • 25) A uniform magnetic field is represented by:
    a) Concentric circles
    b) Parallel lines
    c) Dotted lines
    d) Random curved lines
    Answer: b) Parallel lines
    Explanation: A uniform magnetic field is represented by equidistant parallel lines.

  • 26) Which of the following devices uses a permanent magnet?
    a) Electric motor
    b) Transformer
    c) Galvanometer
    d) Electromagnet
    Answer: c) Galvanometer
    Explanation: A galvanometer has a permanent magnet and is used to detect small currents.

  • 27) A magnetic field is strongest at:
    a) The center of a magnet
    b) The poles of a magnet
    c) The edges of a magnet
    d) Equally throughout
    Answer: b) The poles of a magnet
    Explanation: The magnetic field is strongest at the poles of a magnet where the field lines are denser.

  • 28) The principle behind an electric generator is:
    a) Heating effect of current
    b) Magnetic effect of current
    c) Electromagnetic induction
    d) Chemical effect of current
    Answer: c) Electromagnetic induction
    Explanation: An electric generator works on electromagnetic induction, where a changing magnetic field induces a current.

  • 29) If the direction of current in a straight conductor is reversed, what happens to the direction of the magnetic field?
    a) It remains unchanged
    b) It reverses
    c) It increases in strength
    d) It disappears
    Answer: b) It reverses
    Explanation: According to the Right-Hand Thumb Rule, reversing current reverses the direction of the magnetic field.

  • 30) What happens when a conductor is moved perpendicular to a magnetic field?
    a) No effect
    b) A current is induced
    c) The conductor heats up
    d) The resistance increases
    Answer: b) A current is induced
    Explanation: According to Faraday’s Law of Electromagnetic Induction, moving a conductor in a magnetic field induces a current.

  • 31) A transformer is used to:
    a) Convert DC to AC
    b) Change the voltage of an AC supply
    c) Store electric charge
    d) Convert electrical energy to mechanical energy
    Answer: b) Change the voltage of an AC supply
    Explanation: A transformer increases or decreases AC voltage but does not work with DC.

  • 32) Which part of an electric motor reverses the direction of current?
    a) Armature
    b) Commutator
    c) Brushes
    d) Stator
    Answer: b) Commutator
    Explanation: The commutator reverses current direction, ensuring continuous rotation in a DC motor.

  • 33) Which of the following statements is NOT true for magnetic field lines?
    a) They form closed loops
    b) They cross each other
    c) They have a direction from north to south outside the magnet
    d) They represent the strength of the magnetic field
    Answer: b) They cross each other
    Explanation: Magnetic field lines never cross each other, as this would mean two different directions at one point.

  • 34) An electric generator converts:
    a) Chemical energy to electrical energy
    b) Electrical energy to mechanical energy
    c) Mechanical energy to electrical energy
    d) Electrical energy to heat energy
    Answer: c) Mechanical energy to electrical energy
    Explanation: A generator uses mechanical motion (rotating coil) to generate electricity.

  • 35) What happens if a coil is rotated faster in a generator?
    a) The output voltage decreases
    b) The frequency of AC increases
    c) The direction of current reverses
    d) The coil stops moving
    Answer: b) The frequency of AC increases
    Explanation: Increasing rotation speed increases the frequency and voltage output.

  • 36) What is the role of carbon brushes in a DC motor?
    a) Reduce friction
    b) Provide electrical contact with the commutator
    c) Increase resistance
    d) Generate electricity
    Answer: b) Provide electrical contact with the commutator
    Explanation: Carbon brushes maintain electrical contact between the commutator and external circuit.

  • 37) Which of the following produces a changing magnetic field?
    a) A stationary magnet
    b) A current-carrying conductor
    c) A moving magnet
    d) Both b and c
    Answer: d) Both b and c
    Explanation: A current-carrying conductor and a moving magnet produce changing magnetic fields, which induce current.

  • 38) Which scientist discovered electromagnetic induction?
    a) James Clerk Maxwell
    b) Michael Faraday
    c) Hans Christian Ørsted
    d) Isaac Newton
    Answer: b) Michael Faraday
    Explanation: Faraday’s Law explains how a changing magnetic field induces a current.

  • 39) The Earth behaves like a:
    a) Temporary magnet
    b) Permanent magnet
    c) Electromagnet
    d) No magnet at all
    Answer: b) Permanent magnet
    Explanation: The Earth’s core generates a permanent magnetic field.

  • 40) If the north pole of a magnet is brought near another north pole, they will:
    a) Attract each other
    b) Repel each other
    c) Form a stronger magnet
    d) Cancel each other
    Answer: b) Repel each other
    Explanation: Like poles repel each other, while unlike poles attract.

  1. 41) What happens if the number of turns in a solenoid is increased while keeping the current constant?
    a) The magnetic field decreases
    b) The magnetic field remains unchanged
    c) The magnetic field increases
    d) The solenoid stops working
    Answer: c) The magnetic field increases
    Explanation: The magnetic field of a solenoid is directly proportional to the number of turns. More turns create a stronger field.

    42) In an electric motor, which force is responsible for the rotation of the coil?
    a) Electrostatic force
    b) Magnetic force
    c) Gravitational force
    d) Nuclear force
    Answer: b) Magnetic force
    Explanation: A current-carrying coil in a magnetic field experiences a force due to the interaction between the magnetic field and current.

    43) Which of the following is NOT a method to increase the strength of an electromagnet?
    a) Increasing the number of turns in the coil
    b) Increasing the current
    c) Using a soft iron core
    d) Using a plastic core
    Answer: d) Using a plastic core
    Explanation: Plastic is a non-magnetic material and does not help in increasing the strength of an electromagnet.

    44) A device that converts AC voltage into a higher or lower AC voltage is called a:
    a) Generator
    b) Transformer
    c) Motor
    d) Battery
    Answer: b) Transformer
    Explanation: A transformer changes AC voltage levels using electromagnetic induction.

    45) Which type of transformer is used in mobile chargers?
    a) Step-up transformer
    b) Step-down transformer
    c) Power transformer
    d) Auto-transformer
    Answer: b) Step-down transformer
    Explanation: Mobile chargers use step-down transformers to reduce high AC voltage to lower AC voltage.

    46) Which of the following is NOT an example of electromagnetic induction?
    a) A moving magnet inducing current in a coil
    b) A generator producing electricity
    c) A battery producing electricity
    d) A transformer working on AC supply
    Answer: c) A battery producing electricity
    Explanation: A battery generates electricity through a chemical reaction, not electromagnetic induction.

    47) Which type of magnet is used in an electric bell?
    a) Permanent magnet
    b) Temporary magnet
    c) Electromagnet
    d) Bar magnet
    Answer: c) Electromagnet
    Explanation: Electric bells use electromagnets, which generate magnetism when current flows.

    48) A strong electromagnet is used in:
    a) Electric bulbs
    b) Loudspeakers
    c) Solar panels
    d) Mirrors
    Answer: b) Loudspeakers
    Explanation: Loudspeakers use electromagnets to convert electrical signals into sound.

    49) Which of the following is NOT a property of magnetic field lines?
    a) They form closed loops
    b) They never intersect
    c) They are strongest at the poles
    d) They always move in a straight line
    Answer: d) They always move in a straight line
    Explanation: Magnetic field lines curve around the magnet and do not travel in a straight line.

    50) In an AC generator, the direction of induced current changes:
    a) Once per second
    b) Once in every half rotation of the coil
    c) Once in every full rotation of the coil
    d) Never
    Answer: b) Once in every half rotation of the coil
    Explanation: In an AC generator, the direction of current changes every half rotation due to the reversing magnetic field.

    51) Which of the following statements is true about an electric generator?
    a) It converts mechanical energy into electrical energy
    b) It converts electrical energy into mechanical energy
    c) It produces chemical energy
    d) It stores electrical energy
    Answer: a) It converts mechanical energy into electrical energy
    Explanation: Generators work on electromagnetic induction and convert mechanical motion into electricity.

    52) What will happen if a strong magnet is moved inside a coil?
    a) A current is induced in the coil
    b) The coil loses its resistance
    c) The coil stops working
    d) Nothing happens
    Answer: a) A current is induced in the coil
    Explanation: A moving magnet inside a coil induces current due to electromagnetic induction.

    53) What is the function of slip rings in an AC generator?
    a) To maintain electrical contact with external circuits
    b) To reverse the current direction
    c) To increase voltage
    d) To generate electricity
    Answer: a) To maintain electrical contact with external circuits
    Explanation: Slip rings in an AC generator provide continuous connection without reversing current.

    54) Which of the following is an advantage of AC over DC?
    a) AC is easier to store
    b) AC can be transmitted over long distances with less energy loss
    c) AC requires batteries
    d) AC cannot be generated easily
    Answer: b) AC can be transmitted over long distances with less energy loss
    Explanation: AC voltage can be stepped up or down using transformers, reducing transmission losses.

    55) Which of the following devices contains an electromagnet?
    a) Refrigerator
    b) Electric fan
    c) Doorbell
    d) Solar panel
    Answer: c) Doorbell
    Explanation: Doorbells use electromagnets to create mechanical motion for ringing.

    56) Which of the following statements is correct about Earth's magnetic field?
    a) The north pole of a magnet points to Earth's magnetic south pole
    b) Earth's magnetic poles never change
    c) Earth's magnetic field is caused by static charges
    d) Earth's magnetic field is artificial
    Answer: a) The north pole of a magnet points to Earth's magnetic south pole
    Explanation: Earth's geographic north pole is its magnetic south pole, which attracts the north pole of a magnet.

    57) Which type of magnetism disappears when the current is switched off?
    a) Permanent magnetism
    b) Induced magnetism
    c) Ferromagnetism
    d) Paramagnetism
    Answer: b) Induced magnetism
    Explanation: Induced magnetism (in electromagnets) disappears when current is switched off.

    58) If the current in a conductor is doubled, the strength of the magnetic field around it will:
    a) Double
    b) Remain the same
    c) Become half
    d) Become zero
    Answer: a) Double
    Explanation: The magnetic field is directly proportional to the current.

    59) Which of the following is an application of electromagnetic induction?
    a) Battery
    b) Transformer
    c) LED light
    d) Speaker
    Answer: b) Transformer
    Explanation: Transformers use electromagnetic induction to change voltage levels.

    60) Which phenomenon explains the working of a microphone?
    a) Electromagnetic induction
    b) Heating effect of current
    c) Photoelectric effect
    d) Chemical effect of current
    Answer: a) Electromagnetic induction
    Explanation: Microphones convert sound waves into electrical signals using electromagnetic induction.

Exercise MCQs Solutions

  1. 1) Which of the following correctly describes the magnetic field near a long straight wire?
    a) The field consists of straight lines perpendicular to the wire.
    b) The field consists of straight lines parallel to the wire.
    c) The field consists of radial lines originating from the wire.
    d) The field consists of concentric circles centered on the wire.
    Answer: d) The field consists of concentric circles centered on the wire.
    Explanation:

    • The magnetic field around a current-carrying straight conductor forms concentric circles centered around the wire, as described by Ampere’s Circuital Law and the Right-Hand Thumb Rule.

    • If you point your right-hand thumb in the direction of the current, your curled fingers represent the direction of the magnetic field.
      Hence, option (d) is correct.​

2) At the time of a short circuit, the current in the circuit:
a) Reduces substantially.
b) Does not change.
c) Increases heavily.
d) Varies continuously.
Answer: c) Increases heavily.
Explanation:

    • A short circuit occurs when the live wire and neutral wire come into direct contact, causing low resistance and allowing excessive current flow.

    • This sudden increase in current can damage appliances and cause fire hazards.
      Hence, option (c) is correct.

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