Switches
Switches are used to turn on and turn off electrical circuits. When the
switch is off it prevents the electric current to flow. When the switch
is on, it completes the circuit allowing the electric current to flow.
Make it work
Switches can work in different ways. A switch can turn the buzzer on and
off or it can be use for special patterns of signals. Here's the four
different types of switch that may work for you.
You will need:
- 4.5-volt batteries
- bulb holders
- balsa wood
- paper clips
- thumbtacks
- aluminum foil
- thin copper strips
- wire
- bulbs
- cardboard
- tape
- cork
- pencil
- alligator clips
- X-Acto knife
Simple switch
This is a simple on/off switch. When it is on, the current flows through
the circuit; when it is off, the current stops. Wire up a simple
circuit, but leave a break in the wires. Make a
switch using a block of balsa wood, a paper clip, and
two metal thumbtacks. When the clip touches both thumbtacks, the switch
is on.
Pressure switch
This type of switch can be used to make a doorbell ring when someone
steps on
a doormat. Wire up a circuit as before. Fold a piece of cardboard in
half. Wrap strips of foil around each half of the cardboard so that they
touch when pressed together. Tape the wires to the foil on the outside
of each side of the cardboard. When the strips of foil touch, the switch
is on.
Dimmer switch
Electricity can pass through the graphite in a pencil, but it is hard
work. Graphite is called a resistor, because it offers resistance to the
electric current. You can use a graphite pencil resistor to make a
dimmer switch. The longer your pencil lead, the more resistance there is
and the dimmer your light will be.
Tapper switch
This switch is used by Morse code operators. It gives the operator total
control over the length of time the circuit is complete or broken. The
switch is on when the two strips of copper are pressed together. It
returns automatically to the "off" position when not in use.
Create a simple circuit and fit alligator clips to the free
ends of the wire. Soak a pencil in water and then ask an adult to slice
it open down the middle with an X-Acto knife. Attach the alligator clips
to opposite ends of the pencil lead; gradually slide one clip toward the
other.
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