Manual

38
Diffuse lighting
A good mirror is pretty ex-
pensive. Why not try it with a piece of
paper?
You will need
Black paper, white paper
Experiment
1. Hold the white sheet of paper in the full sun
a few centimeters away from a shaded wall.
The wall close to the paper will appear brighter,
but only slightly so. You won’t see a clearly
bright spot.
2. Repeat the experiment with the black paper.
Now the wall doesn’t look any brighter at all.
Explanation
The black paper swallows up almost all the light
and therefore doesn’t light up the wall at all.
The white paper, on the other hand, reflects
back almost all the light that hits it — which is
why it looks bright white to us. But it scatters
the light: The originally parallel rays are steered
in all directions by the rough paper surface.
Can heat be reflected?
If the aluminum foil redirects
the sun’s light, can it do that with heat as well?
You will need
Thermometer, solarium annex cover, aluminum
foil, tape
Experiment
1. Set the solarium cover on the table and lay
a piece of aluminum foil on top of it, with the
dull side toward the cover. Smooth out the foil
and secure it to the cover with tape. Now the
shiny side is nice and flat and can easily be used
as a mirror.
2. Hold the thermometer in a shady location
for a few minutes in order to measure the air
temperature, and make a mental note of it.
3. Then use the aluminum foil to direct sunlight
to the bulb of the thermometer — but don’t let
direct sunlight hit it. After a few minutes, take
a reading of the temperature.
Explanation
Even reflected sunlight can increase the ther-
mometer temperature quite a bit. Apparently,
then, the heat of the sun is reflected too.
Focused heat rays
In Experiment 55, you saw how
to focus rays of light by using a certain
shape of mirror. Maybe you can do that with
heat rays too.
You will need
Thermometer, small concave mirror from the
cutout sheet, aluminum foil, scissors, glue
Experiment
1. Cut out the small concave mirror from the
cutout sheet and glue aluminum foil to its back,
shiny side down. The foil should be as smooth
as possible.
2. Pull the ends over one another to form a
cone-shaped structure with the aluminum foil
on the inside, and secure it with glue.
3. Hold the concave mirror in the sun and use
your hand or a small piece of paper to deter-
mine where most of the reflected rays meet.
That will be the brightest spot, and you will
even be able to feel a little warmth with your
hand.
4. Push the thermometer into the concave mir-
ror from below so that as many reflected rays as
possible hit the thermometer bulb, but as little
direct sunlight as possible. As you do this, hold
EXP.
56
EXP.
57
EXP.
58