# Electromagnetic Induction

Card 1: Electromagnetic Induction

## Electromagnetic Induction

When a magnet is moved into and out of the solenoid, magnetic flux is being cut by the coil.

The cutting of magnetic flux by the wire coil induces an e.m.f in the wire.

When the solenoid is connected to a closed circuit, the induced current will flow through the circuit.

Card 2: Factors affecting the magnitude of the induced e.m.f. - Faraday,s Law

Faraday's Law states that the magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux through a coil or alternatively the rate of the magnetic flux being cut.

Card 3: Determining the direction of the induced current - Lenz's Law

## Lenz's Law

Lenz's Law states that the induced current always flows in the direction that opposes the change in magnetic flux.

Card 4: Determining the direction of the induced current - Fleming's Right Hand Rule

## Fleming's Right Hand Rule (Generator Rule)

Fleming's Right-Hand Rule is used to determine the direction of the induced current that flows from the wire when there is relative motion with respect to the magnetic field

Card 5: Direct Current Generator

## Direct Current Generator

A simple d.c generator essentially the converse of a d.c. motor with its battery removed.

Card 6: DC Generator - Display of the Voltage in a CRO

## DC Generator - Display of the Voltage in a CRO

• Initially the armature is vertical. No cutting of magnetic flux occurs and hence induced current does not exist.
• When the armature rotates, the change in flux increases and the induced current correspondingly increases in magnitude.
• After rotating by 90°, the armature is in the horizontal position. The change in magnetic flux is maximum and hence the maximum induced e.m.f is produced.
• When the armature continues to rotate, the change in flux decreases. At the 180° position, there is no change in flux hence no induced current exists.The induced current is achieves its maximum value again when the armature is at 270°. After rotating 360°, the armature returns to its original position.

The current in the external circuit always flows in one direction. This uni-directional current is known as direct current.
Card 7: Alternating Current Generator

## Alternating Current Generator

Generator can be modified to an a.c generator by replacing its commutators with two (separate) slip rings. The two slip rings rotate in tandem with the armature. Carbon brushes connect the armature to the external circuit.

Card 8: AC Generator - Display of the Voltage in a CRO

## AC Generator - Display of the Voltage in a CRO

• The armature is initially at the vertical position. No magnetic flux is cut and hence no induced current exists.
• When the armature rotates, the change in magnetic flux increases and the induced current increases until its maximum value at the horizontal position.
• As the armature continues on its rotation, the change in magnetic flux decreases until at the vertical position, no induced current exists.
• Subsequently upon reaching the horizontal position again, the induced current is maximum, but the direction of the induced current flowing through the external circuit is reversed.
• The direction of the induced current (which flows through the external circuit) keeps on changing depending on the orientation of the armature.
• This induced current is also known as alternating current. The current is positive (+) in one direction and negative in the other (-). The slip rings play a critical role in the generation of alternating current.
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