Waves we can’t see…
EM Spectrum
• The electromagnetic spectrum is the entire
range of EM waves.
• It is divided into regions according to the
length of the waves.
• All EM waves travel at the same speed in a
vacuum – but the wavelength and frequency
differ
EM Spectrum
• The EM spectrum goes from low
frequency/high wavelength to high
frequency/low wavelength
Radio Waves
• Have the longest wavelength/lowest
frequency of all EM waves
• Any EM wave that has a wavelength of longer
than 30 cm is classified as a wavelength.
• Radio stations encode sound information into
radio waves by varying the waves’ amplitude
or frequency – this change is called
modulation. (AM or FM radio stations)
AM vs. FM
AM –
longer wavelengths than FM
Can bounce off the atmosphere
Can travel farther
FM –
less affected by electrical noise – so
sounds transferred are clearer and sound better
TV
• Television signals are also carried by radio
waves.
• Most use shorter wavelengths and higher
frequencies than radio stations
• TV stations use FM waves to carry sound and
AM waves to carry pictures
Microwaves
• Shorter wavelengths and higher frequencies
than radio waves
• Wavelength between 1 mm and 30 cm.
• Cell phones use microwaves
• Signals sent between Earth and satellites use
microwaves.
• Radar also uses microwaves (Radio Detection
and ranging) – used to detect speed of
objects.
Infrared Waves
• Shorter wavelengths and higher frequencies than
microwaves. Wavelengths are between 700
nanometers and 1 mm. (nanometer is
.000000001m)
• Suns rays are infrared – this is what heats your
body. The waves cause the particles in your skin
to vibrate more, creating heat.
• Almost all objects give off infrared waves
• Not visible to naked eye, but there are infrared
cameras that will detect them
Visible Light
• A very narrow range of wavelengths and
frequencies that humans can see
• Wavelengths between 400 nm and 700 nm
• Some energy from the sun is visible light –
called white light. White light is a
combination of all visible light wavelengths
Colors
• Humans see the different wavelengths of
visible light as different colors.
• Longest wavelength is red – shortest is violet
• This range of colors is called the visible
spectrum
• ROY G BIV
Ultraviolet Light
• Wavelengths vary between 60nm and 400 nm
• Bad effects on humans – UV light causes
sunburns, skin cancer, wrinkles, and damage to
eyes
• Good effects on humans – UV waves kill bacteria
on food and other objects. Cause skin cells to
produce vitamin D which allows the intestines to
absorb calcium
• Most UV light waves are blocked from reaching
Earth by the Earth’s atmosphere.
X-Rays
• Wavelengths between .001 nm and 60 nm.
• Because they are so small, they can pass
through many materials, including human soft
tissue.
• X-Ray machines used for security and medical
Gamma Rays
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Shortest wavelengths – shorter than .1nm
Can penetrate most materials very easily
Used to treat some forms of cancer
Also used to kill bacteria in foods