Elenco Snaptricity® - Manual (Page 31)

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Educational Corner:
Light Bulb Project #21
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?
Incandescent bulbs like these
make light by passing a big
electric current through a
special high-resistance wire,
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.
Electric Paths
Do you want to learn more?
Incandescent bulbs produce lots of heat, and the
glass bulb prevents the filament from reacting with
oxygen in the air and burning. When the voltage
rating of an incandescent bulb is exceeded, the
filament gets so hot it burns out. Filaments are
usually made of tungsten, since ordinary copper
would melt.
The fluorescent light bulbs that come in white 4 ft.
tubes are the standard room lights for offices and
schools. They pass electric current through a gas,
usually argon. This gas emits light as the electricity
passes through it, similar to how a tungsten wire
does. Although larger and more expensive than
ordinary incandescent lamps, they are typically five
times more efficient at converting electricity into light.
The difference in heat produced between
incandescent and fluorescent light bulbs might
surprise you. Find a fluorescent bulb and feel the
heat coming off it; you won’t feel much. Find an
incandescent lamp THAT HAS BEEN OFF FOR A
WHILE and turn it on. Feel the heat it produces; it
soon becomes too hot to touch. Only about 5% of
the electricity used by incandescent bulbs is
converted into light. Without the more efficient
fluorescent bulbs, our society of office buildings might
have been much different.
Build the circuit and hold
down the button on the press
switch (S2). Two lamps (L4)
are very dim while one is
bright.
Operation
All the electric current flows through the top
lamp, then divides between the two lamps on
the left. The top lamp is much brighter than the
others because it has twice as much
electricity flowing through it.
Description
Snappy says: most of
the electrical energy
used by these bulbs
becomes heat, not
light.