Transcript Electromagnetic Induction

Review…
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Direction of magnetic field lines?
Field around a current carrying wire
F = BIL
F = Bqv
Electromagnetic Induction
• We already know current produces magnetic fields.
• Michael Faraday wanted to know if magnetic fields
could induce current.
• He placed a wire loop, which was part of a closed
circuit, into a magnetic field.
• When the wires moves up, the current is in one
direction.
• When the wires moves down, the current is in the
opposite direction.
• When the wire is held stationary or is moved parallel
to the magnetic field lines, there is no current.
• The process of generating current this way is
electromagnetic induction.
• https://www.youtube.com/watch?v=txmKr69jGB
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How does this work?
• In order to produce current, you need electrical
energy.
• Electromotive Force- (EMF) voltage
– NOT A FORCE!
• When the wire moves through the B-field, you
exert force on the electrons and they move in the
direction of the force.
• Work is done on the electrons.
• They increase their electrical potential energy =
current
EMF
• Depends on
– Magnitude of B-field
– Length of wire in B-field
– Velocity of wire in B-field
Generators
• https://www.youtube.com/watch?v=rnPEtw
QtmGQ
Generators
• Invented by Faraday
• Converts mechanical energy to electrical energy
• Wire loops wrapped around iron is placed in a
strong B-field.
• The iron makes B-field stronger
• Iron + wire loops = armature
• Increasing loops will increase EMF
• Connecting the generator to a circuit and the
induced EMF will produce an electric current.
• Generators and motors are almost identical.
• Generators convert mechanical energy to electrical
energy
• http://phet.colorado.edu/en/simulation/faraday
• Motors convert electrical energy into kinetic
energy
Lenz’s Law
• Induced current flows in a direction to
oppose the change that produced it.
• If a generator produces a small current, then the
opposing force will be small and the armature
will be easy to turn.
Transformers
• Device used to increase or decrease AC
voltage
• Change voltages without losing a lot of
energy
• Has 2 cells that are insulated from each other, but
wound around the same iron core.
• Primary Coil and Secondary Coil
• When primary coil is connected to AC voltage,
the changing current creates a varying B-field.
• The B-field is carried through the iron core to the
secondary coil.
• In the secondary coil, the B-field causes a varying
EMF
• Mutual Inductance
• https://www.youtube.com/watch?v=VucsoEhB0
NA
Exit Slip
• In your own words, describe how a
generator works using a fuel source we
talked about today (coal, hydro, etc.).
Include key words: mechanical energy,
current, magnetic field, induce.