Lesson #29

Lesson #29
E.Q: What is electromagnetism?

Electromagnetism

Multiple Choice

The relationship between electricity and magnetism is called _____________.

• Electricity

• Law of Conservation of Energy

• Electromagnetism

• Magnetism

Multiple Choice

A _______________ is a coil that carries an electric current. 

• Solenoid

• Simple Electric Motor

• Electromagnet

• Generator

Multiple Choice

What can be done to increase the number of magnetic objects that an electromagnet picks up?

• Make the wire longer

• Remove the nail from the center of the wire

• Increase the number of coils in the solenoid

• Spread the coils out across the nail

Multiple Choice

A generator is a machine that transforms ____________ energy to ______________ energy.

• Electrical to Mechanical

• Mechanical to Electrical

• Radiant to Mechanical

• Mechanical to Thermal

Multiple Choice

A simple motor converts ______________ energy to ____________ energy. 

• Magnetic to Electrical

• Electrical to Magnetic

• Electrical to Mechanical

• Mechanical to Electrical

Electromagnetic Induction

We know an electric current can be induced by a magnetic field

• Is it possible to do the reverse?

• Is it possible to use a magnetic field to generate an electric current?

• Answer: Yes!

Electromangetic induction

• Electromagnetic induction is the process of inducing a current in a circuit by changing the magnetic field that passes through the circuit

• In electromagnetic induction, a changing magnetic field induces a current

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  If the magnet is withdrawn from the coil then an e.m.f. is induced in the opposite direction.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

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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

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

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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