Class 10 Science Chapter 12 Question Answers - Magnetic Effects of Electric Current

Q1: Define electromagnetic induction and explain Faraday's law of electromagnetic induction. Describe an experiment to demonstrate the generation of induced current using a coil and a magnet.
Ans: Electromagnetic induction is the process by which an electromotive force (emf) or voltage is induced in a conductor when it is exposed to a changing magnetic field. Faraday's law of electromagnetic induction states that the magnitude of the induced emf is directly proportional to the rate of change of magnetic flux through a closed loop of wire.
Experiment to Demonstrate Induced Current:

• Take a coil of insulated wire and connect its ends to a galvanometer (a sensitive current detector).
• Place a bar magnet near the coil and keep it stationary.
• Observe the galvanometer for any deflection or induced current.
• Move the magnet quickly towards the coil and then away from it. Note the direction of the deflection in the galvanometer.
• Repeat the process by moving the magnet in different directions and at varying speeds.

Explanation:

• When the magnet is moved toward the coil, the magnetic field through the coil increases, inducing a current in the coil in a specific direction.
• When the magnet is moved away from the coil, the magnetic field through the coil decreases, inducing a current in the opposite direction.
• The induced current is temporary and occurs only when there is a change in magnetic flux.

Q2: Describe the working principle of an electric generator. Explain how an electric generator converts mechanical energy into electrical energy with the help of a labeled diagram.
Ans: An electric generator is a device that converts mechanical energy into electrical energy through electromagnetic induction. It operates based on Faraday's law of electromagnetic induction.
Working Principle:

• Mechanical Energy Input: An external mechanical force (such as a turbine's rotation) is applied to a coil of wire within a magnetic field.
• Changing Magnetic Field: As the coil rotates, the magnetic field through the coil changes, causing a change in magnetic flux.
• Induced EMF: According to Faraday's law, the changing magnetic flux induces an electromotive force (emf) or voltage across the coil.
• Current Generation: The induced voltage drives an electric current to flow through the coil and the external circuit connected to it.

Labeled Diagram:

  N      Coil of Wire     S       Magnetic Field

  |-----------------------|       |-------------|

  |                       |       |             |

  |                       |       |             |

  |        Mechanical     |       |             |

  |        Energy Input   |       |             |

  |                       |       |             |

  |                       |       |             |

  |-----------------------|       |-------------|

Q3: Define the term "magnetic field" and explain its direction around a current-carrying conductor. Describe an experiment to verify the direction of the magnetic field using a magnetic compass.
Ans: A magnetic field is the region around a magnet or a current-carrying conductor where the influence of magnetism can be detected. It exerts a magnetic force on other magnets or moving charges.
Direction of Magnetic Field around a Current-Carrying Conductor:

• Around a straight current-carrying conductor, the magnetic field forms concentric circles perpendicular to the conductor. The direction is determined using the right-hand rule: If the thumb of the right hand points in the direction of the current flow (from positive to negative), the curled fingers indicate the direction of the magnetic field.

Experiment to Verify the Direction of the Magnetic Field:

• Place a straight current-carrying conductor (such as a wire) on a flat surface.
• Place a magnetic compass near the conductor, parallel to the surface.
• Pass current through the conductor in a specific direction (e.g., from left to right).
• Observe the deflection of the compass needle.

Explanation:

• The magnetic field created by the current causes the compass needle to deflect. The deflection indicates the direction of the magnetic field lines around the current-carrying conductor, which is perpendicular to the surface.

Q4: Describe the construction and working of an electric motor. Explain how an electric motor converts electrical energy into mechanical energy with the help of a labeled diagram.
Ans: An electric motor is a device that converts electrical energy into mechanical energy by utilizing the principle of electromagnetic induction. It operates based on Ampere's law and Fleming's left-hand rule.
Construction and Working:

• Magnetic Field: A strong magnetic field is created by placing a permanent magnet between the poles of another magnet.
• Commutator: A split ring (commutator) is attached to the coil, allowing the current to change direction every half rotation.
• Coil: A coil of insulated wire (armature) is mounted on an axle within the magnetic field.
• Brushes: Carbon brushes press against the commutator and provide a continuous connection to the external circuit.

Labeled Diagram:

       N                  N

   ___[ ][ ][ ][ ]___    [ ] Axle

  |   \   |   /   |      |\

  |    \  |  /    |      | \ Brushes

  |     \ | /     |      |  \

  |      \|/      |      |   \___

  |_______A_______|      |       S

                           Permanent Magnet
Working:

• Current Flow: When current flows through the coil, an electromagnetic force is generated according to Ampere's law.
• Armature Movement: The magnetic force interacts with the external magnetic field, causing the armature to rotate.
• Commutator Action: As the armature rotates, the commutator reverses the direction of the current in the coil every half rotation.
• Continuous Rotation: The alternating current in the coil and the interaction with the magnetic field result in continuous rotation of the armature.

The conversion of electrical energy to mechanical energy in an electric motor allows it to perform various tasks, from operating appliances to driving machinery.

Q5: Explain the concept of the magnetic field and its lines of force. Describe the behavior of a magnetic compass needle when placed near a current-carrying conductor. Provide an example of how the right-hand thumb rule is used to determine the direction of the magnetic field around a current-carrying conductor.
Ans: Magnetic Field and Lines of Force:

• A magnetic field is the region around a magnet or a current-carrying conductor where the influence of magnetism can be detected. It is represented by imaginary lines called magnetic lines of force.
• Magnetic lines of force are continuous loops that indicate the direction of the magnetic field. They emerge from the north pole of a magnet and enter the south pole, forming closed loops.

Behavior of a Magnetic Compass Needle near a Current-Carrying Conductor:

• When a current flows through a conductor, a magnetic field is created around it.
• If a magnetic compass needle is placed near the current-carrying conductor, it aligns itself perpendicular to the direction of the magnetic field lines.

Example of Using the Right-Hand Thumb Rule:

• Hold the current-carrying conductor in your right hand, with your thumb pointing in the direction of the current flow (from positive to negative).
• Curl your fingers around the conductor. The direction in which your fingers curl indicates the direction of the magnetic field lines around the conductor.

For instance, if the current flows from your thumb toward your fingers, the magnetic field lines circulate clockwise around the conductor. If the current flows from your fingers toward your thumb, the magnetic field lines circulate counterclockwise around the conductor.
The right-hand thumb rule is a handy tool to determine the direction of the magnetic field around a current-carrying conductor and helps in understanding the behavior of magnetic fields in various situations.

Q6: Explain the concept of electromagnetic induction and its applications. Describe how a changing magnetic field induces an electromotive force (emf) in a closed loop of wire. Provide an example of electromagnetic induction used in everyday life.
Ans: Electromagnetic induction is the process by which an electromotive force (emf) or voltage is induced in a closed loop of wire when the magnetic field through the loop changes. This phenomenon is the basis for generating electricity in power plants and various other applications.
Process of Electromagnetic Induction:

• Changing Magnetic Field: When a magnetic field through a closed loop of wire changes due to relative motion between the field and the loop, an emf is induced in the loop.
• Faraday's Law: The induced emf is directly proportional to the rate of change of magnetic flux through the loop. Mathematically,  ϵ = − dt/dΦ, where ϵ is the induced emf and dt/dΦ is the rate of change of magnetic flux.

Example of Electromagnetic Induction:

Transformers used in power distribution systems rely on electromagnetic induction. When alternating current (AC) flows through one coil (primary coil) of a transformer, it generates a changing magnetic field. This changing magnetic field induces an emf in another coil (secondary coil) placed close to the primary coil. The induced emf in the secondary coil can be used to increase (step-up transformer) or decrease (step-down transformer) the voltage for efficient power transmission.

Q7: Describe the working of an electric motor and explain how it converts electrical energy into mechanical energy. Discuss the role of the commutator in the operation of an electric motor.
Ans: An electric motor is a device that converts electrical energy into mechanical energy through the interaction of a magnetic field and a current-carrying conductor. It operates based on the principles of electromagnetic induction and Ampere's law.
Working and Conversion of Energy:

• Current Flow: When current flows through a coil of wire (armature) placed within a magnetic field, an electromagnetic force is generated, causing the armature to rotate.
• Commutator Action: The armature is equipped with a split ring called a commutator. As the armature rotates, the commutator reverses the direction of the current every half rotation.
• Continuous Rotation: The changing direction of the current in the armature interacts with the magnetic field, resulting in continuous rotation of the armature.
• Mechanical Output: The rotational motion of the armature can be used to perform mechanical work, such as driving a fan, a conveyor belt, or a vehicle.

Role of the Commutator:

• The commutator is a critical component of an electric motor. It ensures that the direction of the current in the coil changes at the right time to maintain continuous rotation of the armature.
• As the armature rotates, the commutator reverses the connection between the coil and the external circuit, ensuring that the current flows in the appropriate direction to sustain the motor's motion.

Q8: Define the term "magnetic field" and explain its direction around a current-carrying conductor. Describe an experiment to verify the direction of the magnetic field using a current-carrying wire and a magnetic compass.
Ans: A magnetic field is the region around a magnet or a current-carrying conductor where the influence of magnetism can be detected. It exerts a magnetic force on other magnets or moving charges.
Direction of Magnetic Field around a Current-Carrying Conductor:

• Around a straight current-carrying conductor, the magnetic field forms concentric circles perpendicular to the conductor. The direction is determined using the right-hand rule: If the thumb of the right hand points in the direction of the current flow (from positive to negative), the curled fingers indicate the direction of the magnetic field.

Experiment to Verify the Direction of the Magnetic Field:

• Place a straight current-carrying conductor (such as a wire) on a flat surface.
• Connect the conductor to a power source to allow current flow.
• Place a magnetic compass near the conductor, parallel to the surface.
• Observe the deflection of the compass needle.

Explanation:

• The magnetic field created by the current causes the compass needle to deflect. The deflection indicates the direction of the magnetic field lines around the current-carrying conductor, which is perpendicular to the surface.

Q9: Explain the working principle of an electric generator and its role in generating electricity. Discuss the process of electromagnetic induction and how it leads to the production of an induced current in a generator.
Ans: An electric generator is a device that converts mechanical energy into electrical energy through electromagnetic induction. It plays a crucial role in generating electricity for various applications.
Working Principle and Electromagnetic Induction:

• Mechanical Energy Input: An external mechanical force (such as steam turbine rotation or water flow) is applied to rotate a coil of wire within a magnetic field.
• Changing Magnetic Flux: As the coil rotates, the magnetic field through the coil changes, inducing an electromotive force (emf) or voltage across the coil.
• Induced Current: The induced voltage drives an electric current to flow through the coil and the external circuit connected to it.

Process of Electromagnetic Induction:

• According to Faraday's law of electromagnetic induction, a change in magnetic flux through a closed loop of wire induces an emf in the loop. The induced emf is directly proportional to the rate of change of magnetic flux.

Production of Induced Current in a Generator:

• The coil of wire, also known as the armature, is rotated within a magnetic field.
• The changing magnetic field through the armature induces an emf in the coil.
• The induced emf drives an electric current to flow through the coil and the external circuit, generating electrical energy.

Electric generators are essential components of power plants and are used to produce the electricity that powers our homes, industries, and various electronic devices.

Q10: Define "magnetic effects of current" and explain the concept of a solenoid. Describe how the strength of the magnetic field inside a solenoid can be increased. Provide an example of a device that uses the magnetic properties of a solenoid.
Ans: The "magnetic effects of current" refer to the phenomenon in which a current-carrying conductor produces a magnetic field around it. When electric current flows through a conductor, it generates a magnetic field, which can exert a force on other magnets or moving charges.

Concept of a Solenoid:

• A solenoid is a coil of wire wound in the shape of a helix. When a current flows through a solenoid, it generates a magnetic field along its axis.

Increasing the Strength of the Magnetic Field inside a Solenoid:

• The strength of the magnetic field inside a solenoid can be increased by:
• Increasing the number of turns of wire in the coil.
• Increasing the current flowing through the solenoid.
• Using a ferromagnetic core (such as iron) inside the coil, which enhances the magnetic field.

Example of a Device Using the Magnetic Properties of a Solenoid: An electromagnetic relay is a device that uses the magnetic properties of a solenoid. It consists of a coil of wire (solenoid) wrapped around a soft iron core. When current flows through the coil, it generates a magnetic field that attracts a movable armature. This armature can then actuate switches or other mechanical components, allowing the relay to control larger electrical currents or perform various functions in circuits, such as switching on or off lights, motors, or other devices.