#### Transcript Do now!

```Do now!
When do you want the test?!
Today’s lesson - Transformers
Can you gather around Mr
Porter?
Transformers
A changing current in the primary coil
produces a changing magnetic field in the
coil. This changing magnetic field induces
a changing current in the secondary coil.
Changing voltages
The ratio of the number of turns on the
coils equals the ratio of the voltages
# of turns = Np
# of turns = Ns
Vp/Vs = Np/Ns
Changing voltages
A transformer where the voltage rises is
called a step-up transformer
Changing voltages
A transformer where the voltage falls is
called a step-down transformer
No energy for nothing
Power in = power out
VpIp = VsIs
a.c. only
Because transformers rely on induction
(changing fields), they only work with
alternating current (a.c.)
Why do we need transformers?
Current flowing through wires causes them
to get hot and energy is lost.
Why do we need transformers?
Keeping the current
low means
electricity can be
transported long
distances without
losing too much
energy.
Why do we need transformers?
However, in order to send a large quantity
of energy, high voltages are needed.
Transmission of Electricity
Step-up
Step-down
Today’s lesson
Practice questions for this topic
Deciding when to have the test!
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