Your solar engine doesn’t only run in bright sunlight. It will also run on bright light from a lamp. Use a 75 Watt incandescent bulb in a desk lamp.
Artificial Clouds
You know the story: it’s a bright sunny day, then it
gets cloudy and the nice weather is over. You have to
go inside if the sky darkens with heavy black thunder-
clouds. And worst of all: your solar engine won’t work.
But why is it that the sunlight on an overcast day isn’t
enough to power the engine?
Experiment 3
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You will need: bright sunlight, your solar model,
a sheet of 8 1/2 x 11-inch transparent paper (white
tracing or wax paper)
Instructions
Hold the transparent paper over your solar module
while the engine is turning. Then fold the paper down
the middle and hold this smaller surface over the
solar cells. Fold the paper again and again, observing
what happens each time you hold it over the solar
module.
Results
When you hold the unfolded thin, transparent sheet
over the solar cell, enough light still gets through and
the engine still turns. When you fold it, the sunlight
has to get through another layer in order to reach the
solar cell. The more you fold the sheet, the more lay-
ers you create. Each layer absorbs some of the light.
When there are too many layers, there isn’t enough
light getting through to the cell and the engine stops.
When the sky gets overcast, the same thing hap-
pens. Layers of clouds come between the Sun and
the Earth. Enough light can still get through a thin
layer of cirrus clouds to power the solar model. But
not enough of the Sun’s rays can get to your model
through thicker layers of cloud cover.
Artificial Sun
As you know, light isn’t only produced by the Sun. A
lamp with an incandescent or halogen bulb can also
provide light. Will this kind of light also run your mo-
tor?
Experiment 4
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You will need: daylight, your solar model, an as-
sortment of lamps in your house
Instructions
On a bright sunny day, turn on several lamps in your
home, such as floor lamps, overhead lights, and desk
lamps. Hold your solar module directly under the
lamps. What happens?
Results
Your solar cells don’t just convert sunlight into electri-
cal current. If a lamp produces enough light, it can
also run the solar engine. In that sense, lamps work
just like an artificial Sun.
Not all of the lamps in your house will provide
enough light. The incandescent bulbs in electric lights
have different levels of strength. The strength of these
kinds of lights are indicated in watts (W). A bulb with
60 watts creates much brighter light than one with 15
watts. Also, some lights use a reflector to focus their
light, creating greater brightness at a specific point.
Reflectors are usually silver-colored.
There are some kinds of lighting that have built-in
reflectors as well as ones that concentrate light.
Because there are so many different kinds of lamps
and lighting, one might be bright enough to run the
engine while another might not.
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