# Electromagnetic Induction  Can a magnet produce electricity?

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Electromagnetic Induction  Can a magnet produce electricity?

Michael Faraday  An English scientist who was first to prove that a magnet can produce current. A magnet can produce electricity! Duh! Joseph Henry

What conditions are necessary for a magnet to produce current?  Magnet must be moving or  Wire must be moving  Movement causes changing magnetic field  Changing magnetic field induces current

Electromagnetic Induction  The phenomenon by which an emf or current induced in a conductor due to change in magnetic field.

What factors affect the nature of emf or current produced?  Direction of motion  In or out  Speed of motion  Polarity of magnet coming in  Number of turns  Area of coil

Direction of Motion  The direction of the current induced opposes the change producing it

Speed of Motion  The faster the movement is, the greater is the induced emf.

Polarity of magnet  The induced current produces a magnetic field that opposes the one causing it.  Use RHR

Number of turns  The more the number of turns, the greater the emf induced.

Laws of EM induction  Faraday’s Law  The induced emf across the conductor is equal to the rate at which magnetic flux is cut by the conductor.

Magnetic Flux  Product of flux density (B) and the area (A), when flux is at right angles to the area.  Ø= BA  Unit: Weber, Wb  A weber is the flux when a unit tesla of magnetic flux density is at right angles to a unit area.

Magnetic Flux Linkage  Total flux cut by all turns of the coil  Ø= BAN

So far…  EMF = d Ø /dt  For single coil  EMF = BA/t  For many coils  EMF = BAN/t  For a wire  EMF = Blx/t  Where l is length of wire and x is distance traveled.  EMF = Blv  Where v is the speed

Lenz’s Law  The direction of any induced current is such as to oppose the change that causes it.

Therefore  EMF = - d Ø /dt  For single coil  EMF = - BA/t  For many coils  EMF = - BAN/t  For a wire  EMF = - Blx/t  Where l is length of wire and x is distance traveled.  EMF = - Blv  Where v is the speed

Example 1  A straight wire of length 0.2 m moves at a steady speed of 3 ms -1 at right angles to a magnetic field of flux density 0.1 T. What will be the emf induced across the ends of the wire?

Example 2  A coil of wire having 2500 turns and of area 1 cm 2 is placed between the poles of a magnet so that the magnetic flux passes perpendicularly through the coil. The flux density of the field is 0.5 T. The coil is pulled rapidly out of the field in a time of 0.1 s. What average emf is induced across the ends of the coil?

Investigating Lenz’s Law

Uses of EM Induction (Generator)

Transformer

Uses of EM Induction

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