electromagnetic induction
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Electromagnetic Induction. AP Physics Chapter 21. Electromagnetic Induction. 21.1 Induced EMF. Induced EMF. Michael Faraday – a changing magnetic field can produce an electric current This is an induced current. 21.1. Induced EMF. - PowerPoint PPT PresentationTRANSCRIPT
Induced EMF
Michael Faraday – a changing magnetic field can produce an electric current
This is an induced current
21.1
Induced EMF
A magnet moved quickly into a coil of wire induces a current
When it is quickly moved the other way, a current is induced in the opposite direction
21.1
Faraday’s Law of Induction; Lenz’s Law
From experiments the induced emf depends on
1. Rate of change of the magnetic field
2. Loop’s area
3. Angle
Magnetic flux is the
total number of
magnetic field line
passing through
the are enclosed by the loop 21.2
Faraday’s Law of Induction; Lenz’s Law
Magnetic Flux
When is 90, no field lines pass through the loop
The unit for magnetic flux
is a weber
21.2
cosBAB
Faraday’s Law of Induction; Lenz’s Law
Since the induced EMF is the rate of change of flux
This is Faraday’s Law of Induction
For multiple loops in a magnetic field
Where N is the number of loops in the field 21.2
tB
tN B
Faraday’s Law of Induction; Lenz’s Law
Lenz’s Law – a current produced by an
induced emf moves in a direction so that its
magnetic field
(produced by
the current)
opposes the
original change
in flux
21.2
Faraday’s Law of Induction; Lenz’s Law
Steps in problem solving – Lenz’s Law
1. Determine if the magnetic flux inside the loop is decreasing, increasing, or unchanged
2. The magnetic field due to the induced current
a. Points in the same direction as the external field if the flux is decreasing
b. Points in the opposite direction if the flux is increasing
c. Is zero if the flux is not changing 21.2
Faraday’s Law of Induction; Lenz’s Law
Steps in problem solving – Lenz’s Law
3. Use the right hand rule-1 to find the direction of the induced current
4. Always keep in mind that there are two magnetic fields
a. An external field whose flux must be changed if it is to induce an electric current
b. A magnetic field produced by the induced current
21.2
Faraday’s Law of Induction; Lenz’s Law
If the rod above is made to move at a velocity v
The area of the rod increases
So the change in area is
The induce EMF is21.3
tvx tlvxlA
tB
t
AB
t
tBlv
Blv
Faraday’s Law of Induction; Lenz’s Law
Sometimes called motional emf
True as long as components are mutually perpendicular
21.3
Changing Magnetic Flux Produces Electric Field
Since there is an induced current when there is an induced EMF, there must be an electric field
A changing magnetic field induces an electric field
So since
And
The electric field must be21.4
qvBF
q
FE
q
qvBE vBE
Electric Generators
Generator – converts mechanical energy (spinning) into AC current.
If we look at just one perpendicular arm of the loop
Since we have two arms in each loop
Now if we add loops
21.5
Generator Simulation
sinBlv
sin2Blv
sin2NBlv