Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 16)

You’ve seen how electricity flows through copper wires
easily and how carbon resists the flow. How well does
water pass electricity? Let’s find out.
Connect the wires according to the Wiring Checklist and
take a look at the schematic. There isn’t a switch this
time, so just disconnect one of the wires if you want to
turn the circuit off. Notice that the Wiring Checklist leaves
2 wires unconnected. The LED will be off initially (if you
touch the two loose wires together then it will be on).
Now take a small cup (make sure it isn’t made of metal),
fill it half way with water, and place the two unconnected
wires into the water without touching each other. The
LED should now be dimly lit, but the brightness could
vary depending on your local water quality. You are now
seeing a demonstration of how water conducts (passes)
electricity. (A small cup of water like this may be around
100K
Ω, but depends on the local water quality). Try
adding more water to the cup and see if the LED
brightness changes (it should get brighter because we
are “making the water pipe larger”). Since the LED only
lights when it is in water now, you could use this circuit as
a water detector!
Now adjust the amount of water so that the LED is dimly
lit. Now, watching the LED brightness, add some table
salt to the water and stir to dissolve the salt. The LED
should become brighter because water has a lower
electrical resistance when salt is dissolved in it. Looking
at the water pipe diagram, you can think of this as a
strong cleaner dissolving paintballs that are mixed in with
the rocks. You could even use this circuit to detect salt
water like in the ocean!
EXPERIMENT #6: Water Detector
Wiring Checklist:
o 27-to-41
o 40-to-39
o 44-to-42-to-38-to-3
o 4-to-unconnected
(use a long wire)
o 26-to-45-to-43-to-
unconnected
(the unconnected
wire should be long)
Water Diagram
On/Off
Valve
Rocks
and
Paintballs
Rocks
Pump
Schematic
Rocks
Rocks
Water
Meter
-16-
Long
Wire to
Water
Long
Wire to
Water