# 30 Lecture

## Electromagnetic Induction

Electromagnetic induction is a phenomenon that occurs when a magnetic field changes over time, producing an electric field and an associated flow of electric charge.

## Important Mcq's Midterm & Finalterm Prepration Past papers included

When a magnet is moved towards a coil of wire, an induced current is produced. What is the direction of the induced current?

A) In the opposite direction to the motion of the magnet

B) In the same direction as the motion of the magnet

C) In a direction perpendicular to the motion of the magnet

D) The direction depends on the strength of the magnet

Answer: A) In the opposite direction to the motion of the magnet

Faraday's law of electromagnetic induction relates which of the following quantities?

A) Electric field and magnetic field

B) Electric field and time-varying magnetic field

C) Magnetic field and time-varying electric field

D) Magnetic field and current

Answer: B) Electric field and time-varying magnetic field

A transformer is a device used to:

A) Store electrical energy

B) Increase or decrease voltage levels in a circuit

C) Convert AC to DC

D) Convert DC to AC

Answer: B) Increase or decrease voltage levels in a circuit

Lenz's law states that:

A) The magnitude of the induced emf is proportional to the rate of change of magnetic field

B) The direction of the induced emf is in the same direction as the change in magnetic field

C) The direction of the induced emf is opposite to the change in magnetic field

D) The direction of the induced emf is perpendicular to the magnetic field

Answer: C) The direction of the induced emf is opposite to the change in magnetic field

Which of the following is not a way to induce an electromotive force in a conductor?

A) Moving a magnet near a conductor

B) Moving a conductor near a magnet

C) Changing the electric field near a conductor

D) Changing the magnetic field near a conductor

Answer: C) Changing the electric field near a conductor

The primary coil of a transformer is connected to a 120 V AC power source. If there are 200 turns in the primary coil and 400 turns in the secondary coil, what is the voltage across the secondary coil?

A) 60 V

B) 120 V

C) 240 V

D) 480 V

Which of the following is a measure of the strength of an induced electric field?

A) Resistance

B) Capacitance

C) Magnetic flux

D) Inductance

An induced current is produced in a coil of wire when:

A) A magnetic field is applied to the coil

B) The coil is connected to a battery

C) The coil is moved through a magnetic field

D) A static magnetic field is present in the vicinity of the coil

Answer: C) The coil is moved through a magnetic field

A metal rod is moved perpendicular to a magnetic field with a velocity of 5 m/s. The rod has a length of 0.2 m and a resistance of 2 ohms. If the magnetic field has a strength of 0.3 T, what is the magnitude of the induced emf?

A) 0.6 V

B) 1.0 V

C) 3.0 V

D) 6.0 V

What is the purpose of a commutator in a DC motor?

A) To convert AC to DC

B) To increase the speed of the motor

C) To reverse the direction of the current in the motor

D) To increase the efficiency of the motor

Answer: C) To reverse the direction of the current in

## Subjective Short Notes Midterm & Finalterm Prepration Past papers included

What is electromagnetic induction?

Electromagnetic induction is the phenomenon of generating an electromotive force (emf) or voltage in a closed circuit due to the change in magnetic flux through the circuit.

What is Faraday's law of electromagnetic induction?

Faraday's law states that the emf induced in a circuit is proportional to the rate of change of magnetic flux through the circuit.

What is Lenz's law?

Lenz's law states that the direction of the induced emf is such that it opposes the change that produced it.

What is self-induction?

Self-induction is the phenomenon of inducing an emf in a coil due to the change in current flowing through it.

What is mutual induction?

Mutual induction is the phenomenon of inducing an emf in a coil due to the change in magnetic flux linked with it, produced by a current flowing in another nearby coil.

What is an induced current?

An induced current is a current that is produced in a closed circuit due to the presence of an induced emf.

What is an inductor?

An inductor is a passive electrical component that is designed to store energy in its magnetic field. It is typically made up of a coil of wire.

What is an inductance?

Inductance is a measure of the ability of an inductor to store energy in its magnetic field. It is measured in units of henries.

What is a transformer?

A transformer is a device that is used to transfer electrical energy from one circuit to another through the principle of electromagnetic induction.

What is eddy current?

Eddy currents are the currents that are induced in a conductor due to the change in magnetic field linked with it. They are often seen as unwanted effects in electrical machines and can cause energy loss in the form of heat.

### Electromagnetic Induction

Electromagnetic induction is a phenomenon that occurs when a magnetic field changes over time, producing an electric field and an associated flow of electric charge. This principle has numerous applications in everyday life, such as in power generation and the operation of electric motors. The discovery of electromagnetic induction is credited to Michael Faraday, who demonstrated the effect through a series of experiments in the early 19th century. Faraday discovered that by moving a magnet through a coil of wire, or by moving a coil of wire through a magnetic field, he could generate an electric current in the wire. The basis of electromagnetic induction is Faraday's law of induction, which states that the magnitude of the induced electromotive force (EMF) in a conductor is proportional to the rate at which the magnetic field changes with respect to time. This can be expressed mathematically as: EMF = -d?/dt where EMF is the electromotive force, ? is the magnetic flux, and t is time. The negative sign in the equation indicates that the induced EMF is in a direction that opposes the change in the magnetic field that produced it, in accordance with Lenz's law. One practical application of electromagnetic induction is in the operation of generators. A generator consists of a coil of wire that is rotated within a magnetic field. As the coil rotates, the magnetic field passing through it changes, inducing an electric current in the wire. This current can be used to power electrical devices. Another application of electromagnetic induction is in transformers. A transformer consists of two coils of wire, called the primary and secondary coils, which are wound around a magnetic core. When an alternating current is passed through the primary coil, it produces a changing magnetic field, which induces an electric current in the secondary coil. The ratio of the number of turns in the primary and secondary coils determines the voltage and current of the output. Electromagnetic induction also has important implications in the field of electromagnetism. It is the basis for the production of electromagnetic waves, such as radio waves and microwaves, which are used in communication and technology. Electromagnetic waves are produced by oscillating electric and magnetic fields, which can be generated by an alternating current flowing through a wire. In conclusion, electromagnetic induction is a fundamental principle in physics that has numerous practical applications. The ability to generate an electric current from a changing magnetic field has revolutionized the field of electrical engineering and has led to the development of many technological innovations. The discovery of electromagnetic induction is a testament to the power of scientific curiosity and the importance of experimentation in advancing our understanding of the natural world.