Correct Answer: C) Number of coil turns

The symbol N in Faraday's law represents the number of coil turns. The more turns, the greater the induced electromotive force because the magnetic flux cuts through more turns.

The complete formula for Faraday's law: \(EMF = -N \frac{dΦ_B}{dt}\) where:

• EMF: Induced electromotive force
• N: Number of coil turns
• \(dΦ_B\): Change in magnetic flux
• dt: Change in time

Correct Answer: C) Direction of opposing EMF (Lenz's law)

The negative sign in Faraday's law represents Lenz's law, which states that the direction of the induced electromotive force opposes the change in magnetic flux that produced it.

This means that the induced current will be in a direction that opposes the change in the magnetic field that produced it.

This principle ensures conservation of energy, as the system resists any change in magnetic flux.

Correct Answer: D) Electrical capacitors

Electrical capacitors work by storing electrical energy in an electric field and are not directly related to electromagnetic induction or Faraday's law.

While the other applications all rely on Faraday's law:

• Electric generators: Convert mechanical energy to electrical energy using electromagnetic induction
• Electric transformers: Step up or step down voltage using mutual induction between two coils
• Wireless chargers: Transfer energy through electromagnetic induction between two coils without direct contact

Correct Answer: A) Direct relationship

The relationship between induced electromotive force and the rate of change of magnetic flux is a direct relationship.

According to Faraday's law: \(EMF = -N \frac{dΦ_B}{dt}\)

This means that the induced electromotive force is directly proportional to:

1. The number of coil turns (N)
2. The rate of change of magnetic flux with time (\(\frac{dΦ_B}{dt}\))

The greater the rate of change of magnetic flux, the greater the induced electromotive force, and vice versa.

Correct Answer: B) Number of magnetic field lines passing through a surface

Magnetic flux (Φ_B) is a measure of the number of magnetic field lines passing through a given surface.

Magnetic flux is calculated by the relation: \(Φ_B = B \cdot A \cdot \cosθ\)

Where:

• B: Magnetic field strength (Tesla)
• A: Area (meter²)
• θ: Angle between the magnetic field direction and normal to the surface

The unit of magnetic flux is Weber.

Correct Answer: A) That moving a conductor inside a magnetic field generates electric current

Michael Faraday discovered through his experiments that moving a conductor inside a magnetic field (or changing the magnetic field around a stationary conductor) generates an electric current in the conductor.

This discovery led to the formulation of Faraday's law of electromagnetic induction, which states that the induced electromotive force is proportional to the rate of change of magnetic flux.

Faraday's experiments included:

• Moving a magnet inside a wire coil
• Moving a wire coil inside a magnetic field
• Changing the intensity of the magnetic field around a stationary conductor

Correct Answer: A) EMF = -N dΦ_B/dt

This is the correct formula for Faraday's law of electromagnetic induction:

\(EMF = -N \frac{dΦ_B}{dt}\)

Where:

• EMF: Induced electromotive force (Volts)
• N: Number of coil turns
• \(dΦ_B\): Change in magnetic flux (Weber)
• dt: Change in time (seconds)
• Negative sign: Represents Lenz's law (opposing direction)

This formula means that the induced electromotive force is directly proportional to the number of coil turns and the rate of change of magnetic flux, and its direction opposes the change that produced it.