Download Electromagnetism – Electromagnetic Induction and Transformers

Electromagnetism – Electromagnetic Induction and Transformers
NOTES
Electromagnetic Induction
 When a wire moves in a magnetic field, a _______________ acts on the charges in the wire.
 _______________ is done on the charges, causing the electrons to _______________.
 Magnetic fields can induce a _______________ in a wire!
 For EM induction to occur, the wire or the magnetic field needs to be _______________ or
_______________ in strength.
Galvanometers
 A _______________ is a device that uses electromagnetism to measure very small amounts of
_______________ ( ~5 x 10-5 A).
 The _______________ through the wire loop creates a _______________ field.
 The interaction between the loop’s magnetic field and the permanent magnetic field causes the loop
to _______________.
Electric Generators
 The electric _______________ was invented by Michael Faraday and converts _______________
energy into _______________ energy.
 Generators utilize a wire loop called an _______________ that rotates in the magnetic field. As it
rotates a _______________ is induced.
 Also as the loop rotates, the _______________ and _______________ of the current change,
producing an _______________ current.
Difference in AC/DC Current
 The difference between AC and DC has to do with the _______________ in which the electrons flow.
 In DC, the electrons flow steadily in a _______________ direction, or "forward."
 In AC, electrons keep _______________ directions, sometimes going "forward" and then going
"backward.”
 In the US, electric utilities use a _______________ frequency, meaning that the current alternates
direction (forward to backward and back to forward) 60 times in one second.
Transformers
 The _______________ voltage (on the left) induces a
magnetic field in the core, which creates the _______________
voltage (on the right).
 What makes transformers so useful is that if you change the
_______________ of _______________ from one side to the
other, you change the _______________ in the wire on the
right!
 Transformers can change a _______________ voltage to a
_______________ one, or a _______________ voltage to a
_______________ one.
Step Up Transformer
 _______________ transformer converts a _______________ voltage to a _______________ one.
 If you increase the number of turns on the right, the _______________ coming off the transformer will
increase in proportion.
 The right side has _____ times more turns so the voltage on the right has increased _____ times.
 So the voltage has been stepped up by a factor of _____.
Step Down Transformer
 _______________ transformer _______________ voltage.
 If you _______________ the number of turns on the right, the voltage coming off the transformer will
_______________ in proportion.
 The right side has _____ the number of turns, so the voltage is only _____ as large.
 So the voltage has been stepped down by _____.
Transformer Math
 The ratio of the _______________ of turns is the same as the ratio of the _______________.
 An _______________ transformer, which we will always assume, dissipates no power (waste heat).
The power of the _______________ circuit is equal to the power of the _______________ current.
 We use this assumption about power to find the _______________ in the secondary circuit.
Final Thoughts on Transformers
STEP-UP Transformers
STEP-DOWN Transformers
Why Transmit with AC vs. DC?
 Advantages to using AC:
 By using a step-up transformer to hike the voltage, we are able to _______________ the
_______________ and by lowering current, we are able to use _______________ wires.
 Ultimately, we are able to transfer _______________ farther (higher voltage travels farther),
for less _______________ (cost of wire), with better _______________ (less power lost to heat
caused by resistance).
Transformer Example
 A transformer has 7500 turns on its primary coil and 125 turns on its secondary coil. The voltage across
the primary circuit is 7,200 V.
A. What voltage is being applied across the secondary circuit?
B. If the current in the secondary circuit is 36 A, what is the current in the primary circuit?
C. Is this a step-up or a step-down transformer?
A.
B.
C.