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Light Energy
Summary: This activity demonstrates how light energy
can be converted to electrical and mechanical energy.
Introduction:
You know that electricity
is used in many different ways in our lives. Electric power plants
send electricity to homes, schools, and factories. These plants
are expensive to run and frequently cause pollution. We run other
devices with batteries or electric cells. As you know these eventually
run out of power and we throw them away...more garbage and more
expense. Many people have proposed using the energy from the
sun to run electrical devices. It might be a never-ending source
of electricity---as long as the sun shines.
A nifty device developed to capture
the energy from the sun is a solar cell. In fact, a solar cell
can convert the light energy from the sun into very small amounts
of electrical energy. In this activity, you will use a solar
panel to power an electric motor that turns a small propeller.
Materials:
- silicon solar cell with soldered
leads and motor attached (Radio Shack Cat. No.. 277-1201)
- 60 Watt incandescent lamp with
a shade (if sunlight is not available)
- metric ruler
- light probe
Classroom Management:
This activity is best done
in full sunlight. If this is not possible, students can use a
incandescent lamp to provide the needed light energy within the
classroom. Students are also asked to use a light probe to determine
the minimum amount of light needed to operate the motor.
Safety Concerns:
- CAUTION: Do not look directly
at the sun or the light bulb, lasting damage to your eyes will
result.
- Do not touch the bulb when it
is lit, as severe burns may result.
Activity Steps:
1. Setting up the experiment.
- Use the light probe to determine
the light reading (usually in Lux---unit used by scientists to
describe light intensity) of your lamp. Notice that the reading
changes as you move the probe closer and further away from the
bulb. Remember, never look directly at the bulb.
- To simulate sunlight in the classroom
you will use a lamp with an incandescent bulb within the classroom.
Working with your partner, hold the solar panel up to the bulb.
Have a partner hold the motor with the propeller directed away
from objects or people.
2. At what light level will
the motor stop operating?
- With your group members, design
an experiment to determine the minimum amount of light (according
to the light probe) needed to make the propeller turn. Record
your procedure.
- Repeat the experiment three times
using the metric ruler to measure the minimum distance. Average
your results.
3. Make a general statement
about how light energy can be converted to another form.
Extensions:
Should solar cells be used
in your area? Use the light probe and solar cell outside to determine
how often the propeller would turn throughout the day.
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