Transcript Universal Motor

Electricity & Magnetism
• An electric
current in a wire
creates a
magnetic field.
[http://www.pbs.org/wgbh/nova/magnetic/images/reve-current.gif]
Click here to
view
demonstration
videos.
[http://demoroom.physics.ncsu.edu/multimedia/images/
demos/797Solenoid_and_iron_filings.jpg]
Electricity & Magnetism
• Conversely, a
moving
magnet can
create an
electric current
in a wire.
Click Here for a
Demo
Electric Generators
• Motion is turned into
Electricity
• A “force” spins a
loop of wire inside a
magnet producing
electric current
• This occurs because
of electromagnetic
induction
[http://www.nhn.ou.edu/~jeffery/course/c_energy/energyl/lec0
05/turbine_001_diagram.jpg]
Electric Generators
• Generators normally produce Alternating
Current (AC) which changes the
direction that electrons move. (120 times
per second)
• Batteries produce Direct Current (DC)
where electrons always move the same
direction.
Click Here for an Interactive Example
Electromagnets
• Piece of iron
placed inside a
loop of copper
wire.
• Magnetic field is
present only when
current is flowing
in the wire.
[http://media.fwbell.com/images/electromagnet.gif]
Magnetic poles reverse when current
is switched.
S
N
N
S
[http://www.speakercity.ca/images/diagram.gif]
Click Here for Speaker Demo
Electric Motors
• Electricity is turned
into motion.
• Current is passed
through an
electromagnet so it
turns inside a
“normal” magnet to
produce motion.
Click Here for
Demos
http://upload.wikimedia.org/wikipedia/commons/thumb/0/04/Electri
c_motor_cycle_2.png/300px-Electric_motor_cycle_2.png
Electric Motors
• For DC motors,
the commutator
switches the
current in the
electromagnet.
Transformers
• These change
the voltage of
alternating
current.
Click Here for an
Interactive Demo
[http://upload.wikimedia.org/wikipedia/en/thumb/1/1c/Polemount-singlephase-closeup.jpg/397px-Polemount-singlephase-closeup.jpg]
Voltage is controlled by the
coils of wire at the ends.
Vout
Vin
Power is the same
[http://www.worsleyschool.net/science/files/transformers/stepdown.gif]
Vout
Vin
[http://www.worsleyschool.net/science/files/transformers/stepdown.gif]
Transformers
• Example:
• What does the voltage change to in the
transformer below?
Vin = 50 V
Vout = ?
Iin = 10 A
Iout = 2.5 A
[http://www.worsleyschool.net/science/files/transformers/stepdown.gif]
First, calculate the power on
the primary side…
Vin = 50 V
Vout = ?
Iin = 10 A
Iout = 2.5 A
[http://www.worsleyschool.net/science/files/transformers/stepdown.gif]
P=VxI
P = 50 V x 10 A
P = 500 W
Power is equal on both sides, so
use the power to calculate Vout…
Vin = 50 V
Vout = ?
Iin = 10 A
Iout = 2.5 A
[http://www.worsleyschool.net/science/files/transformers/stepdown.gif]
500 W = V x 2.5 A
2.5 A
2.5 A
V = 200 V