Transcript Electromagnetic Induction

Electromagnetic
Induction
Faraday’s Law
Induced Emf
A magnet entering a wire causes
current to move with in the wires I =
Emf / R
The induced current increases as the
number of coils and length of coils
increases (N*L)
The induced current increases as the
velocity of the magnet increases (v)
The induced current increases as the
magnetic field increases (B)
I = N*L*vB / R
Induced Emf
Which way will the current flow?
What direction is the magnetic field
changing?
Into the coil
The direction of current will be determined
by the induced magnetic field produced
by the induced current.
The induced magnetic field produced by
the induced current will oppose
The change in magnetic field (B)
This statement is called Lenz’s law
Induced Emf
The induced magnetic field produced by
the induced current will oppose
The change in magnetic field (B)
This statement is called Lenz’s law
a) Magnet into wire
• B field is increasing to the left
• So the current flowing in the wire must
induce a magnetic field to the right
• Current is counter clockwise
Induced Emf
The induced magnetic field produced by
the induced current will oppose
The change in magnetic field (B)
This statement is called Lenz’s law
a) Magnet out of the wire
• Decreasing to the right
• Induced magnetic field must be to the
left
• Current is clockwise
Magnitude of Induced Emf
• Emf = - Change magnetic flux
time
Magnetic flux = equals the amount of B
Field line passing through
a given area A
The more field lines the greater the flux
The greater the area the greater the flux
Chapter 19 and 20
Review
Magnetic properties
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Like poles repel
Opposite poles attract
Field lines are strongest at poles
Field goes from south to North inside a
magnet
• Field goes away from North and towards
south, outside magnet
• Magnets always have two poles
Magnetic properties continued
• The closer the lines are together the
stronger the field
• Magnetic domains are microscopic
magnetic field lines caused from the
movement of electrons
• Domains line up when external magnetic
field is present
• Magnetic field lines per area is called
magnetic flux
Moving charges induce magnetic fields
• Current moving through a straight wire
induces a magnetic field in a direction
according the first right hand rule
X B
I
Current moving in a loop
• When current flows around a loop a magnetic field is
induced according to the second right hand rule
I
B
B X
i
Magnetic Force FB
• A Force is exerted on a wire when a current carrying wire is placed
inside a external magnetic field in a direction according to the third
right hand rule
North
B
F
South
i
Magnitude of force
• F = BIL
B magnetic field
I Current
L Length of wire
• F = qvB
q charge
v velocity
B Magnetic field
Electromagnetic Induction
• A wire moving inside a magnetic field
causes charges to flow in the wire
• The EMF or voltage is induced Emf = IR
EMF electric motive force
• EMF = B x v x L
B Magnetic field increases
V Motion of the wire increases
L Length of the wire increases