ELECTROMAGNETIC INDUCTION

A PowerPoint Presentation by

Akram Habib

© 2014AH

Electromagnetic Induction

Electromagnetic Induction is the process of using magnetic fields to produce voltage, and in a complete circuit, a current.

Michael Faraday first discovered it, using some of the works of Hans Christian Oersted. His work started at first using different combinations of wires and magnetic strengths and currents, but it wasn't until he tried moving the wires that he got any success

Almost 200 years ago, Faraday looked for evidence that a magnetic field would induce an electric current with this apparatus

Electromagnetic Induction

He found no evidence when the magnet was steady, but did see a current induced when the magnet moves up and down .

Electromagnetic InductionFaraday’s Law

Electromagnetic InductionFaraday learned that if you change any part of the flux over time

you could induce a current in a conductor and thus create a source of EMF (voltage, potential difference). Since we are dealing with time here were a talking about the rate of change of FLUX, which is called Faraday’s Law.

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Electromagnetic Induction

Faraday’s Law

In order to understand Faraday’s law we need to understand the concept of magnetic flux.

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Electromagnetic InductionMagnetic Flux:Magnetic flux is the quantity of magnetic field that penetrates an

area at right angles to it.

Flux is a general term associated with a FIELD that is bound by a certain AREA. So MAGNETIC FLUX is any AREA that has a MAGNETIC FIELD passing through it.

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We generally define an AREA vector as one that is perpendicular to the surface of the material. Therefore, you can see in the figure that the AREA vector and the Magnetic Field vector are PARALLEL. This then produces a DOT PRODUCT between the 2 variables that then define flux.

Electromagnetic Induction

Lenz’s Law The direction of the emf and thus the current is given

by Lenz’s law. The statement in bold in the center of page 789 is a statement of Lenz’s law. Use this to find the direction of the current. If you are looking down on the loop from above, is the current flowing clockwise or counter clockwise?

Electromagnetic InductionLenz’s Law

The magnetic is moving away from the coil so the magnetic field is decreasing, thus the current is in a direction to off-set the decrease.

The magnetic is moving toward the coil so the magnetic field is increasing, thus the current is in a direction to off-set the increase.

Electromagnetic InductionProblem A circular wire loop with a radius of 20 cm. is in

a constant magnetic field of 0.5 T .

What is the flux through

the loop if the normal to

the loop makes an angle

of 300 with the magnetic

field?

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Electromagnetic Induction

In summary

Faraday’s Law is basically used to find the MAGNITUDE of the induced EMF. The magnitude of the current can then be found using Ohm’s Law provided we know the conductor’s resistance.

Lenz’s Law is part of Faraday’s Law and can help you determine the direction of the current provided you know HOW the flux is changing

Electromagnetic InductionUseful Applications

AC Generators use Faraday’s law to produce rotation and thus convert electrical and magnetic energy into rotational kinetic energy. This idea can be used to run all kinds of motors. Since the current in the coil is AC, it is turning on and off thus creating a CHANGING magnetic field of its own. Its own magnetic field interferes with the shown magnetic field to produce rotation.

Electromagnetic Induction

Transformers work only if the current is changing; this is one reason why electricity is transmitted as AC.

Electromagnetic InductionAn Induction Stove

The water in the metal pot is boiling. Yet, the water in the glass pot is not boiling, and the stove top is cool to the touch. The stove operates in this way by using electromagnetic induction.

Magnetic data storage encodes information in a pattern of alternating magnetic fields. When these fields move past a small pick-up coil, the changing magnetic field creates an induced current in the coil. This current is amplified into a sequence of voltage pulses that represent the 0s and 1s of digital data.

How is a credit card reader related to magnetism?

Electromagnetic Induction