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Unit 9: Light Page 13

What’s ‘infrared’? What are all the different

kinds of light?
When you press the
button on your Photons with the lowest amounts
remote control to of energy and longest wavelengths
your TV, you’re (some are the size of football
using infrared light fields) are radio waves. The next
(IR) to control your TV. Infrared step up are microwaves, which
light has a bit more energy that have more energy than radio
microwave light, but it’s still waves. IR has slightly more
invisible to our eyes. energy, and visible light (the

rainbow you can see with your
However, snakes can detect IR and
eyes) has more energy and shorter
see the redder hues that we can’t.
wavelengths. Ultraviolet (UV) light
Every warm body gives off light in
has more energy than visible, and
the IR, so snakes use this to find
x-rays have even more energy
mice in the cool night.
than UV, and finally the deadly
gamma rays have the most
Why can’t I see most kinds
amount of energy.
of light?
A Brief History of light
Different detectors are sensitive to
different colors. Your eyeballs are In the early 1800s, Thomas
sensitive to specific colors in the Young’s double-slit experiment
400-700 nm (nanometer) range showed the world that light was a
(which is how long one wavelength wave.

is. A nanometer is extremely tiny!

The frequency of red light is

around 430 trillion Hz (Hertz,
which is one wave cycle per
second). If you were to count the
number of waves passing a certain
point in one second, you’d count
430 trillion waves. If you counted
750 trillion waves, the light would
be violet. Different colors have
He aimed sunlight through two
different frequencies.
very narrow slits and found a

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