Elenco R/C Snap Rover&reg - Manual (Page 20)

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Project #19
OBJECTIVE: To show how water conducts electricity.
Build the circuit at left and connect the jumper wires to it,
but leave the loose ends of the green and yellow jumpers
lying on the table initially. Turn on the slide switch (S1) -
the LED (D4) will be dark because the air separating the
jumpers has very high resistance. Touch the loose
jumper ends to each other and the LED will be bright,
because with a direct connection there is no resistance
separating the jumpers.
Now take the loose ends of the green and yellow jumpers
and place them in a cup of water, without letting them
touch each other. The LED should be lit, indicating you
have detected water!
For this experiment, your LED brightness may vary
depending upon your local water supply. Pure water (like
distilled water) has very high resistance, but drinking water
has impurities mixed in that increase electrical conduction.
Water Detector
Project #20
OBJECTIVE: To show how adding salt to water changes water’s
electrical characteristics.
Build the circuit at left and connect the jumper
wires to it, but place the loose ends of the
green and yellow jumpers in a cup of water as
in the preceding project. Turn on the slide
switch (S1), the LED (D4) should be dimly lit.
Slowly add salt to the water and see how the
LED brightness changes, mix it a little so it
dissolves. It will become very bright as you add
more salt. You can use this bright LED
condition as a saltwater detector! You can then
reduce the LED brightness by adding more
water to dilute the salt.
Take another cup of water and try adding other
household substances like sugar to see if they
increase the LED brightness as the salt did.
Salt Water Detector
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