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Unit 9: Light Page 25
3. Tape a piece of tracing paper The pencil isn’t really broken, but it
over the cutout side, keeping it sure looks like it! What’s going on?
taut and smooth.
When a beam
4. Make a pinhole in the box side
of light hits a
opposite of the tracing paper.
different
5. Point the pinhole at a window substance (like
and move toward or away from the the water), the
window until you see its image in wavelength
clear focus on the tracing paper. changes
because the speed of the light
OPTIONAL: You can hold up a
changes. If you’re thinking that the
magnifying glass in front of the speed of light is always constant,
pinhole to sharpen the image. you’re right… in a vacuum like
outer space between two reference
Experiment: Light Tricks
frames.
When light rays strikes a surface, But here on Earth, we can change
part of the beam passes through the speed of light just by shining a
the surface and the rest reflects
light beam through different
back, like a ball bouncing on the
materials, like water, ice, blue
ground. Where it bounces depends sunglasses, smoke, fog, even our
on how you throw the ball. own atmosphere. How much the
light speed slows down depends on
Have you ever looked into a pool of
what the material is made of.
clear, still water and seen your own
Mineral oil and window glass will
face? The surface of the water acts
slow light down more than water,
like a mirror and you can see your
but not as much as diamonds do.
reflection. (In fact, before mirrors
were invented, this was the only
How broken the pencil appears also
way people had to look at
depends on where you look. In
themselves.) If you were
some cases, you’ll see a perfectly
swimming below the surface, you’d intact pencil. Other times, you’ll
still see your own face – the mirror
guess neither piece is touching.
effect works both ways. This is why not everyone can see a
rainbow after it rains. The sun
Have you ever broken a pencil by
must be at a low angle in the sky,
sticking it into a glass of water?
and also behind you for a rainbow
to appear. Most times, you aren’t
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