Magnetic Induction

​Click here for Magnetic Effect of Current

​Magnetic Field: The magnetic field is the area around a magnet in which the effect of magnetism is felt.

Magnetic Field Lines: ​Imaginary lines originating from North Pole and entering to south pole.

Magnetism and Electric Current

⚫ A solenoid is a coil
of wire with an
electric current in
it.

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The electric
current creates a
magnetic field
around each loop of
the wire.

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more loops = more
magnetic force

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more current =
more magnetic
force

Magnetism and Electric Current

⚫
The magnetic
force of a solenoid
can also be
strengthened by
adding a soft iron
core to its center.

⚫

This is called an
electromagnet.

Creating Electric Current

⚫
Faraday’s Lawof
Induction describes
the production of a
current in a
conducting circuit by
a change in the
strength, position, or
orientation of an
external magnet.

Electromagnetic Induction

The effect of producing electricity from magnetism was discovered in 1831 by Faraday and is called electromagnetic induction. It led to the construction of generators for producing electrical energy in power stations.

​The principles of electromagnetic induction:

The process of generating electricity from motion is called as electromagnetic induction.

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A coil of wire and a magnet, moving relative to each other are needed to induce a voltage across the ends of the wire.

When the coil and the magnetic field move relative to each other, a current flows through the coil if it is a part of a complete circuit. This is known as an induced current.

The actual reason why a current is induced is because the rotating coil cuts through the magnetic field lines.​

​If the bar magnet is pushed into a coil of wire, an e.m.f. is induced in the coil.  If the magnet is withdrawn from the coil then an e.m.f. is induced in the opposite direction.

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​electromagnetic induction experiment: https://www.youtube.com/watch?v=hajIIGHPeuU​

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The induced e.m.f. (and current) can be increased by: 

(1) moving the magnet or wire faster; 

(2) using a stronger magnet; 

(3) increasing the turns on the coil.

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​Click here for Magnetic Effect of Current

​Properties of Magnetic Field Lines:

• The direction of the magnetic field lines is from the south pole to the north pole.

• Magnetic field lines never intersect with each other.

• Magnetic field lines form a closed-loop.

• Field lines have both direction and magnitude at any point on the field

Creating Electric Current

⚫
Electrical generators change mechanical
energy to electrical energy using
electromagnetic induction.

In a commercial generator, an electric current is
produced when a large coil of wire is rotated
through a strong magnetic field.

Creating Electric Current

⚫
Electricity from a generator changes
direction moving back and forth in cycles.
This is called alternating current (AC).

⚫
Electricity from a Batteries only moves in one
direction This is called direct current (DC).

​a.c Generator:

• A generator converts mechanical energy to electrical energy. ​

• a.c generator generates alternating current.​

• Works based on the electromagnetic induction which states that ​ whenever there is a change in the number of magnetic field lines passing through a conductor, voltage is induced in it.

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​Constructions/parts:

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​Armature Coil

WParts:

• An a.c. generator consists of an armature coil made up of several turns of insulated copper wire wound over a soft iron core, strong magnetic field, slip rings and carbon brushes.

  Working:

• The armature coil is made to rotate in a strong magnetic field as shown in the previous slide.

• As the coil rotates due to external force such as water in hydropower plant, the number of magnetic field lines passing through the coil changes. Hence an emf or voltage is induced in the circuit.

​Graphical Representation of induced emf/current

​Graphical Representation of the induced current/induced emf

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Click here to watch a video​

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​Graphical Representation of induced emf/current

• ​As the coil rotates, the number of magnetic field lines passing through the coil continuously changes.

• The number of magnetic field lines passing through the coil is maximum when the coil is perpendicular to the field lines and minimum when the coil is parallel to the field lines.

• The magnitude of the induced emf is maximum when the coil is parallel to the field lines as at that time, the rate of change of the ​magnetic field lines is maximum and the induced emf is minimum when the coil is perpendicular to the field lines owing to the minimum amount of the rate of change of magnetic field lines.

​ Transformer

​An electrical device used for varying(change) the voltage of an alternating current is called transformer.

​ Transformer

​Transformers are of:

1. Step-Up Transformer-increased the voltage from low to high

2. Step-down Transformer​-decreased the voltage from high to low

​ Transformer (Sketch)

​ Differences between step up and step down transformer