Data Sheet

Project 74 Transformer
Build the circuit as shown. Assemble the build-your-own electromagnet
as per the instructions on page 5. Push the wire on the build-your-own
electromagnet to one side and insert its iron rod into the top of the elec-
tromagnet (M3), as shown. Set the meter (M5) to the 1mA setting.
Push the press switch (S2) and hold it down for a few seconds; the
relay (S3) makes a buzzing sound as its contacts open and close
quickly. Watch the white LED (D6) and meter, then reverse the direc-
tions of the LED and meter and push the switch again (it works better
in one direction, depending on how you wired the build-your-own elec-
tromagnet). If the LED does not light in either position then you may
need to push the iron rod further into the M3 electromagnet.
Pull the iron rod out the M3 electromagnet. The LED should no longer
light when you press the switch, because the magnetic connection be-
tween the circuits is broken now.
You can replace the build-your-own electromagnet with the one made
with the red jumper wire in project 52 (wind the red wire on one side of
the rod), but it will not work as well because it has less windings.
If a current through a coil can
magnetize an iron bar, what if you
had another coil from a different
circuit wrapped around the same
iron bar? The magnetization of the
iron bar would create a current in
the other circuit. This is a trans-
former, which allows one circuit
to create a current in another cir-
cuit using magnetic fields.
Transformers allow circuits to be
isolated from each
other, since the con-
nection between them
is magnetic and not
electrical. Transform-
ers can also change
the voltage by using
coils with more or less loops of
wire.
When electric power companies
transport electricity across great
distances (like between power
generating plants and cities), they
use very high voltages and low
currents since this reduces power
loss in the wires. Large trans-
formers convert this to 120V,
which is supplied to homes and
offices. Many products (like com-
puters) then use small transform-
ers to convert this to smaller or
larger voltages as needed.
A transformer is a magnetic
bridge, since we use magnetism
to cross an air gap that electricity
cannot cross by itself.
Iron Bar
Created
Current
Original Current
High Voltage
Power Lines
Transformer
120V House
Power Line
Power Plant
Typical
Transformer
1mA
The buzzing sound produced by
the relay is used to create a con-
stantly changing magnetic field in
the build-your-own electromagnet,
which induces a current in the M3
electromagnet, which is seen on
the LED and meter.
-64-
SC_STEM1_manual_PRINT.qxp_Layout 1 7/13/17 4:45 PM Page 65