1. III. Electromagnetic Induction.
Oersted: Moving charge (I) exerts a _____________________.
N’s 3rd law: A magnet exerts a __________________________ .
force on a magnet
force on a moving charge
magnet Dq S N v v
A: a wire
________
w/ current q
at rest
C: wire with
____________
B: __________
__________
moving
charge
no current
but moving
The charges in ____________________ experience
a _________________ force Fmag.
all 3 cases
magnetic

2. For any charge q moving with a velocity v through a B:
Magnitude (strength) of Fmag:
Fmag = ________________, q is angle between v and B.
Notice: If q = 0, then Fmag = _______ .
Direction of Fmag.
Fmag is _______________________ to v and B.
qvB sinq
perpendicular
Ex: A charged particle moves at different angles to B.
Assume v is the direction of the charge's motion.
450
900 00
q = _____
q = _____
q = _____ z x y z x y z x y
Fmag=0
Fmag B B B
Fmag v v v
max.
med.
min.
Fmag = _______
Fmag = _______
Fmag = _______

3. > > Ex: The force between 2 current-carrying wires is used
to define the ________________:
ampere I
>
wire 1
Fmag
Fmag I
>
wire 2
1 ______________ = the amount of current in two infinite
wires of negligible diameter separated by a distance
of _________________ that will produce a magnetic force of
_______________________ per meter of length.
Note: The force is ___________________ when the current
is in same direction in both wires.
ampere
1 meter
2 x 10-7 N
attractive

4. Case C (again): A wire conductor moved in a B field
the magnet could be moved N S E
Fmag causes the ______________________________________
This ___________________________ an electric field in the
wire, which results in an _______________________________
or _________________________between the ends of the wire.
electrons to move to one end of the wire.
induces (or sets up)
induced potential difference,
induced voltage
Electromagnetic Induction:
“______________ motion between a conductor and a B field
induces (creates) a ___________________ in the conductor.”
Relative
potential difference

5. Because the strength of the _________________ depends on
the angle between the __________________ and the B field,
the amount of induced ______________________ also does.
magnetic force
v of the charge
potential difference
Ex 1. A wire moved between two magnets.
Its velocity v is perpendicular to B: q = ______
900 v N S v
The wire "cuts" _____________________ the most B lines
The angle between v and B is _______ , so Fmag is ________.
____________ potential difference V is induced in the wire.
In symbols: v B 
directly through
900
max.
Maximum
max. V

6. Ex 2. A wire moved at an angle: < q <00
900 v N S v
The wire cuts ________________B field lines.
Because the angle between v and B is ____________
Fmag is ____________________
_______ V is induced in the wire than in previous case.
some
not a max.,
less than max.
Less

7. Ex 3. A wire moved parallel to B: q =00 v v N S
The wire cuts ________________B field lines.
Because the angle between v and B is ____________
Fmag is _____________
_______ V is induced in the wire.
In symbols: v B 
none of the
zero
zero No ||
min. V (=0)

8. induced potential difference 1 2 3 In sum: angle between Case
v and B (0)
induced potential
difference 1 2 3 90
max.
between 0-90
in between
min.
potential
Notice that in all three cases above, a ________________
________________ was set up that is a result of the
________________________ between the wire and B field.
But unless the wire is attached to a circuit, _____________
________________ .
difference
relative motion
no current
will flow

9. Electromagnetic devices use magnetism and electricity:
motors (based on Case _____ from first slide)
 A ___________ in wire experiences a force due to B.
If that force can be made to ____________________, then you can transform: A
current
turn a coil of wire
______________ energy  _______________ energy
electrical
mechanical
Another example of this is a ___________________
It is a ______________________ that is attached to a
paper cone. When current passes through the wire,
the magnetic force makes the paper cone move.
speaker
coil of wire
______________ energy  _______________ energy
 _______________ energy
______________ energy  _______________ energy
electrical
mechanical
sound

10. Simple DC motor
Instead of
permanent
magnets,
you can use
the current
from the
battery to
create
electromagnets
to provide the
B field. F v B B v F

11. 2. generators (based on Case _____ from first slide)
 When a wire with no current is moved, the Fmag pushes the ____________ to the ends of the wire, but ___________________unless the wire is ______________
__________________ C
electrons
no charge flows
connected
to a circuit: N S v
current
With a complete circuit, there is ______________, and
_____________ energy  ______________ energy
mechanical
electrical

12. A
simple AC
generator:
Instead of
permanent
magnets,
you can use
some of the
output current
to create
electromagnets
to provide the
B field.

13. B field has a constant direction, so Fmag depends
on the direction of v: F B v B v F
The electromagnetic
force pushes charges
out the "short" wire
turn
counter-
clockwise

14. Now coil has turned so that it is vertical:B B v
No force on electrons
or induced voltage
because v and B
are parallel (or anti-
parallel)
turn
counter-
clockwise

15. Now coil has made another ¼ turn or so…F B v B v F
The electromagnetic
force pushes charges
out the long end –in
other words…in the
opposite direction!!!
turn
counter-
clockwise

16. Then you would
see something
like this:
And, as the coils
were turned, it
would look like:
Now imagine looking
straight down the
rings

17. B always left
Direction of induced current: I t
This is
how AC m a d e ! I t I t I t

18. Electrical motors and generators are basically the _______
devices—they have _________ that turn in _____________:
same
wires
B fields
motor
generator
________________ out
mech. energy
electric energy
______________ out
_______________ in
mech. energy
________________ in
electric energy

19. Instead of moving a
wire through a B field
to induce a voltage,
you can also change the
B field near the wire by
______________________
moving the magnet
Credit cards have a unique ____________ strip Moving the card changes the __________ in the ATM.
This induces a unique ____________ in a coil in the ATM.
4. Guitar pickups are coils wrapped around ___________.
When a ____________ guitar string vibrates, it changes the
__________ of the magnet. This induces a _______________
in the coil which is amplified and sent to a _____________ . .
magnetic
B field
voltage
magnets
steel
B field
voltage
speaker

20. 5. Transformers  two ________________ wrapped
5. Transformers  two ________________ wrapped around the same ____________:
wire coils
iron core
iron
core AC
primary
______current in _______________ coil causes…
…the __________ at ________________ coil to change…
…which induces a ______________________________
in the _________________ coil.
B field
secondary
potential difference (voltage)
secondary
If N2 ___ N1, then voltage is ___________________________ .
>
stepped up (increased)
<
stepped down (decreased)

21. VoutIout VinIin = created destroyed
Energy is neither _______________ nor _______________ :
Power in =
Pin =
VinIin =
Power out
Pout
VoutIout
Step up:
VinIin =
VoutIout
VoutIout
Step down:
VinIin =
Voltages are ____________________ for long-distance
transmission because less heat or ________ energy
is lost. Once they reach their destination, they are _____________________ for safe use.
stepped up
I2R
stepped down

22. 6. In antennas:
________________are accelerated _________________
As a result, ________________________ radiation
is emitted from the antenna as ____________.
The radiation is made up of:
1/ an ____________ field and
2/ a _____________ field
As they move, the fields are constantly
________________ . As one field changes,
it induces _______________________________ .
These waves move out ________________
_____________ . Radio waves, __________________
and ___________ are all forms of ___________________ _________________ and travel at the speed of __________ .
electrons
up and down
electromagnetic
waves
electric
magnetic
changing
the other field and vice versa
at the speed
of light
visible light
x-rays
electromagnetic
radiation
light

23. This is an example of electromagnetic ________________ .
In this way, __________ waves can transmit ___________
by means of their _______________ through a vacuum.
induction
E & M
energy
fields
When these fields reach an antenna, the fields
force the _________________ in the antenna to accelerate
at the exact same _______________ .
Cell phones and microwave ovens also transmit
energy by means of electromagnetic ____________.
electrons
frequency
waves