Data Sheet

Project 31
Light Bulb
Build the circuit. Turn on the
slide switch (S1) on and off
several times, watching the
brightness of each lamp
(L4). Compare the bright-
ness of each lamp, and
how quickly each turns on.
All the electric current flows through the right lamp, then divides between the two lamps
on the left. The right lamp is much brighter than the others because it has twice as much
electricity flowing through it, but that is not the only reason for the difference in brightness.
Why is the top lamp so much brighter than the others, even though it only has twice as
much electricity through it? And why do the left bulbs take a few seconds before they make
any light?
This happens because a dim light bulb has less resistance than a bright one. Incandescent
bulbs like these make light by passing a big electric current through a special high-resis-
tance wire, the filament. The high current heats up the filament, which gets so hot that it
glows. The left bulbs get less current than the top one so they take longer to heat up and
don’t get as hot, barely getting hot enough to light their filaments.
How much brighter is the right lamp compared to
the others?
Why do the two lamps on the left turn on
slowly?
Project 30
OR Circuit
if switch S9, switch S1 OR switch S2
is on then the lamp will be on. Engi-
neers refer to this
switching combi-
nation as an OR sub-circuit (short
for “this OR that”). The same type
of circuit is used throughout your
home, such as having several
sensors controlling a security light.
Place the magnet next to the reed switch
(S9) to turn it on, push the press switch
(S2), and turn on the slide switch (S1) in
different combinations while seeing if the
lamp (L4) lights. Fill out this table with
the results:
S9 S1 S2 L4
OFF OFF OFF
OFF OFF ON
OFF ON OFF
OFF ON ON
ON OFF OFF
ON OFF ON
ON ON OFF
ON ON ON
Are the three switches connected in series or in parallel?
Give an example of an OR circuit in your home.
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