Trafo

Transformers
Any time the voltage of alternating current needs
to be changed, a transformer is used to change
it. One example is changing the very high voltage
coming from power lines to the lower voltage for
your home. These transformers usually are large,
and can be found on telephone poles or on the
ground as seen at right.
As electricity is sent from the power plant across
the state, it loses some voltage along the way. To
bring the voltage back up, larger sets of transformers
are located in substations, to accomplish
that.

Another example is for changing the 120 volts from
an electrical outlet to a lower voltage for a video
game. These transformers are the small, squarish
looking black adapters that come with many low voltage
devices, such as the one at right

how does trafo work?

How does a Transformer Work?
1. Electricity moving through the primary coil creates a magnetic
field.
2. This magnetic field induces (causes to happen) an electric
field and moves electrons in the secondary coil, thus producing
an electric current.


Primary coil Voltage = Secondary coil Voltage
# turns of wire in primary # turns of wire in secondary
Sample Problem 1:
Incoming (primary) voltage = 120 V
# turns of wire in primary = 75
# turns of wire in secondary = 150
Outgoing (secondary) voltage = ?
Sample Problem 1:
Incoming (primary) voltage = ? V
# turns of wire in primary = 9
# turns of wire in secondary = 30
Outgoing ( secondary) voltage = 400 V
Transformers that decrease the voltage are called step-down
transformers.
Transformers that increase the voltage are called step-up
transformers.