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)
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