Electromagnetism: Inquiry 4
Motor Effect
Faraday's Law
Lenz's Law
Motors and Generators
An induced emf always gives rise to a current that creates a magnetic field that opposes the original change in flux through the circuit.
The induced emf in a circuit is equal in magnitude to the rate at which the magnetic flux through the circuit is changing with time.
resultant force
conductor in magnetic field
Magnetic Flux
amount of magnetic field in area
Φ = B||A = BA cos θ
weber, Wb. 1 Wb = 1 T m2.
EMF
Electromotive Force
provides energy
make current flow
ε=(-(Φ_f-Φ_1))/Δt=(-ΔΦ)/Δt
o where Φ, f is the final flux and Φ, i is the initial flux. ε has units of T m2 s−1, which is the same as volts, V.
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Work is done on any free electrons by the induced electric field
Law of Conservation of Energy
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Magnetic Braking
magnet moved over metal
induce emf
induce eddy currents
slows down magnet
DC Motor
current-carrying coil
in magnetic field
Torque
rotational force
stator, rotor, commutator
speed limited by back emf
Causes back emf
AC Induction Motor
producing a rotating magnetic field
a device that transforms electrical potential energy into rotational kinetic energy
Generator
Output emf is always positive
DC generator
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transforms mechanical kinetic energy into electrical energy
converts electrical energy into mechanical energy