Electromagnetic Induction(EMI)

AP Physics

Electromagnetic Induction (EMI)A changing magnetic field can induce a current in a circuit

called the induced current.

The corresponding emf that must be present to cause the current is the induced emf.

What Causes Induction

Magnetic Flux (φm)The amount of magnetic field there is in an area. (The number

of magnetic field lines in an area.)

Units of φm:

Only the components of

magnetic field that are perpendicular

to the area contribute to the

flux.

θ

Magnetic Flux (φm)

θθ

θ

Faraday’s LawBut wait…to have induction there must be a change in the magnetic field

(therefore a change in the magnetic flux)!!

“The induced emf in a circuit equals the rate of change of the magnetic flux through the circuit.”

Flux ProblemThe U-shaped conductor lies perpendicular to a uniform magnetic field B

with magnitude B = 0.60 T, directed into the page. We lay a metal rod with length L = 0.10 m across the two arms of the conductor, forming a conducting loop, and move the rod to the right with constant speed v = 2.5 m/s. What is the magnitude of the resulting emf?

GeneratorsA device that converts mechanical energy to electrical energy.

Alternating current generator (alternator)

Lenz’s Law“The direction of any magnetically induced current or emf is such as to

oppose the direction of the phenomena causing it.”

Lenz’s LawLenz’s Law requires some thinking!

Motional emfThe induced emf in a circuit equals the rate of change of the

magnetic flux through the circuit.

TransformersA device that converts voltage.

Power Transmission

Physics Rock BandElectromagnetic Induction is used to ROCK

OUT!!• Microphones

Physics Rock BandElectromagnetic Induction is used to

ROCK OUT!!• Electric Guitar

Physics Rock BandElectromagnetic

Induction is used to ROCK OUT!!

• Cassette Tapes (kickin’ it old school)