Instructions

19
9 An electric tester
In this experiment, a test device is built to check which things
conduct electricity. The resistance of 10k Ω (brown, black,
orange) should further reduce the current through the LED,
as great brightness is not required here. There are two cables
with test tips. You can use these to touch any object. When
the LED lights up, you know that electricity is flowing through
it. All metals conduct electricity, but also other things such as
pencil lead.
Even weak conductors are detected. If you touch both wires
with your fingers, you will see a very dim light. So, the skin
does conduct some electricity. If you moisten your fingers
with water, even more electricity will be conducted. This is
harmless because the battery only has a voltage of 9V. How-
ever, high voltages over 48 V can be dangerous. The mains
voltage of 230 V is life-threatening! You may touch wires only
if you know for certain that the voltage is no more than 12V.
In addition to a test object, the push button switch can also
close the circuit. This helps to distinguish whether the object
being examined is a good or bad conductor. When the test
cables touch an object, the LED will light up. Then press on
the button. Does the LED shine even brighter? In this case, it
is a weak conductor. But if you examine a metal object or a
wire, there will be no difference, because all metals are good
conductors.