Transcript EMI (97-03)

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.)
Only the
components of
magnetic field that
are perpendicular
to the area
contribute to the
flux.
Units of φm:
θ
Magnetic Flux (φm)
θ
θ
θ
Faraday’s Law
But 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 Problem
The 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?
Generators
A 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 Law
Lenz’s Law requires some thinking!
Motional emf
The induced emf in a circuit equals the rate of change of the
magnetic flux through the circuit.
Transformers
A device that converts voltage.
Power Transmission
Physics Rock Band
Electromagnetic Induction is used to ROCK
OUT!!
• Microphones
Physics Rock Band
Electromagnetic Induction is used to
ROCK OUT!!
• Electric Guitar
Physics Rock Band
Electromagnetic
Induction is
used to ROCK
OUT!!
• Cassette Tapes
(kickin’ it old
school)