use of this light. Even when just a little enters in, it
can be used to produce electricity. But most of the
time, it will be too weak to start the engine. The more
light that reaches the solar cell, the more electricity it
produces. Starting at a certain level of brightness, the
cell will produce enough electricity to run the engine.
During the day, sunlight combines with the light from
the lamp. That is why the engine runs at a greater
distance from the lamp than in the evening. After the
Sun sets, there is no more daylight and the light from
the lamp has to run the solar engine by itself.
Reverse Movement
Up to now, your solar engine has only run in one
direction. Now we’ll find out how to make it run in
reverse.
Experiment 7
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You will need: your solar model
Instructions
Run your model in bright sunlight. Watch the direc-
tion that the small sprocket wheel turns. Then remove
both electric cables from either the engine or the bat-
tery holder and plug them back in, but this time in the
opposite sides. Hold your model in bright light again.
What happens?
Results
After you reverse the cables, the wheel turns in the
opposite direction. That is because electrical current
always flows in just one direction. The engine rotates
in the same direction that the current flows. The
direction of flow can be changed by reversing the cur-
rent supply — which is exactly what you do when you
switch the cables. It makes no difference whether you
switch them at the battery holder or the engine. The
direction of current flow is determined by the solar
cell. Remember what you read on page 7 about how
solar cells work?
If the solar module is turned around, the current flows in the opposite
direction. That makes the rotation direction of the engine change, too
(see the text on p. 13).
You can change the rotation direction of the engine by reversing the
connections of the cables to either the engine or the battery holder.
The rotation direction of the engine follows the direction of the flow
of current. The solar module producing the current determines its
direction of flow (see the text on p. 13).
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