Fill in the blanks with the words provided.
Bones
Light
PIR
Shortest
Gamma rays
Longest
Radio waves
Soft Tissue
Thermal imaging
Wavelength
Ultraviolet
Infra-red
Microwaves
Radiotherapy
Speed cameras
Vacuum
X-rays
Let's start with the lowest-frequency waves Radio waves. These
have the Longest wavelength of all the waves in the EM spectrum.
Next come Microwaves. As well as for mobile phones, they are
used for Speed cameras. They have a Wavelength of a few
centimetres.
Next are the waves that we feel as heat Infra-red waves. "PIR"
detectors pick up these waves if someone approaches, and will
trigger a security light or a burglar alarm. Emergency services may
use Thermal imaging cameras to reveal where casualties may be
stuck under rubble.
Light is the only part of the electromagnetic spectrum that we can
see directly. It travels at 300 million metres per second - but then
again so do all the other EM waves. Also, all EM waves can cross
a Vacuum.
"Blacklights" aren't really black - they give off Ultraviolet waves that
our eyes can't see, but they make some substances fluoresce
(glow).
Wilhelm Roentgen discovered X-rays. These waves are absorbed
by Bones, but pass easily through Soft tissue, revealing the
structure of the body.
Finally we come to the waves with the Shortest wavelength
Gamma waves. They can be used to kill cancer cells, we call this
Radiotherapy.