Manual Part 2

35
CAUTION: very warm lamp enclosure.
Project 18 | ELECTRIC HEATER
Turn on the slide switch (S1), cover the
holes in the top of the lamp (L4) with
your nger, and wait. After a minute
or so you should feel the lamp heating
up. Do not leave the circuit for two
minutes because the lamp will be hot.
Part B: Instead of placing the red & black jumper wires in
water, touch the metal part of each with your ngers, using
your body to complete the circuit. Wet your ngers to get
better electrical contact. The white LED (D6) should be on,
but brightness may vary.
There is no danger in touching the circuits you build with
Snap Circuits because of the low-voltage batteries they use
(4.5V). But the electricity from your electric company is a
much higher voltage (120V), and it can seriously injure and
even kill you if it enters your body. This is why it is important
that you never touch a wire without disconnecting it from
the electricity (by turning it off and unplugging it) or without
placing proper insulation (materials that electrons cannot
travel through) between you and the wire (which is why most
of the wiring inside appliances has a colorful plastic coating).
Because tap water is conductive (low resistance), dropping
a live wire (a wire that is plugged into your house’s
electricity) into your bath connects every wet part of your
body to the 120V electricity owing through the wiring in
your house.
Distilled (or ltered) water has almost no impurities (or things other than
water molecules) in it. Because of this, distilled water has a very high electrical
resistance, meaning that current doesn’t ow through it easily.
The water that comes out of your tap has chlorine, uoride and other chemicals
to make it safe for you to drink. Because of these impurities, tap water has a
low electrical resistance, meaning that current ows through it rather easily.
Adding salt (sodium chloride) to the water decreases its resistance even more,
because this adds sodium and chloride ions (or moveable charges) to the mix.
This is why it is incredibly important that you don’t enter a swimming pool
when there’s a chance of lightning. If lightning occurs anywhere near the pool,
the high-energy electrons will follow the path of least resistance straight into
the water and, because your body is mostly water, into you.
Incandescent light bulbs like L4
contain a special thin wire that gets
so hot when electricity ows through
it that it glows. Only about 5% of the
electricity used in incandescent light
bulbs is used to make light; the rest
becomes heat, which is why you can
feel the L4 lamp heat up when you
cover its venting holes. Electric space
heaters convert electricity to heat in a
similar way to warm up a room.
Build the circuit as shown,
leaving the ends of the red &
black jumper wires unconnected
for now. Turn on the slide switch
(S1); the white LED (D6) should
be off.
Place the loose ends of the red
& black jumper wires into a cup
of water (but not distilled water),
without them touching each
other. The white LED should be
on now, because water conducts
electricity, completing this circuit.
Try dissolving some salt in the
water or using different liquids,
and see how the LED brightness
changes. You can also replace
the white LED with the color
LED (D8).
Don’t drink any liquids
used here.
Project 19 | WATER COMPLETES CIRCUIT