Carolina Power House Kit - Manual (Page 7)

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the thermometer from the top by the small
ring. Watch the temperature. Within a few
minutes, it will start to rise.
Explanation
The aluminum foil concentrates the captured
solar energy onto one small area, which there-
fore becomes hotter. Even though the concave
mirror is small and doesn’t have a particularly
shiny surface, the effect is quite noticeable.
The bigger, the hotter
The little mirror in the previ-
ous experiment managed to produce
quite a noticeable increase in temperature. Will
the effect be even more noticeable with a big-
ger and better mirror?
You will need
Thermometer, large concave mirror from the
cutout sheet, scissors, aluminum foil, glue
Experiment
1. Cut out the large concave mirror from the
sheet and glue aluminum foil to its back, shiny
side out. The foil should be as smooth as pos-
sible. Glue the ends over one another as in the
previous experiment.
2. Point the concentrated rays at the bulb of the
thermometer, and watch the temperature. It
will rise quickly and dramatically.
Be careful not to let the temperature rise above
100 degrees Celsius, or the thermometer could
get damaged.
Explanation
With its large surface area, this mirror captures
a lot more sunlight than the small one.
Be careful when experimenting with the con-
cave mirror and the sun!
Never look directly into the sun, or you could
suffer eye damage.
Always store the concave mirror with its foil
side down, and never leave it unattended. Do
not leave any ground lenses, such as magnify-
ing lenses or eyeglasses, lying near it. It could
cause a fire!
Concave mirror
This is the name for a mirror that has an in-
ward-curving surface rather than a flat one.
Incoming parallel rays of light are not re-
flected back as a bundle of parallel rays, but
are concentrated together in a tight spot. If
the concave mirror forms a hemisphere, it
creates a shape known as catacaustic, with
the rays failing to meet exactly at one point.
It is only with a so-called parabolic mirror
that they do that, as shown in cross-section
in the drawing. The larger the mirror, the
more of the sun’s rays it can capture and the
hotter it will get at this “focal point.”
In the Pyrenees Mountains in
southern France, there is a giant solar oven
with a concave mirror as tall as a house that
is capable of generating temperatures of
3600 degrees Celsius. It has 63 secondary
tracking mirrors that reflect the sun’s light
into the large concave mirror.
Instead of round mirrors, large solar power
plants usually have parabolic mirrors in
the shape of a channel or “trough.” These
mirrors have a focal line rather than a focal
point, along which pipes carry a special
liquid that is heated by the sun and that
transports the heat to electricity generators.
Parabolic trough power
plant in the California
desert
Energy Saving Tip
Don’t let water run unnecessarily
(while brushing your teeth, for
example).
EXP.
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