Electromagnetic (EM) Spectrum Notes
Electromagnetic spectrum is….
● All the frequencies or wavelengths of electromagnetic radiation.
● Electromagnetic wave is a wave that can travel through a vacuum, like space, and is made up of
both electric and magnetic fields.
● Electromagnetic radiation is created in stars, like our sun, and travels through space.
EM’s Identify Crisis
● Scientific studies of electromagnetic waves conclude that in some situations, electromagnetic
waves act like a particle, and sometimes they act like a transverse wave.
How Electromagnetic (EM) waves move
● EM radiation travels in waves.
● Radiation - the transfer of energy as EM waves
● EM radiation travels in a straight line through a vacuum, like space, but will slow down and
travel at different speeds when it enters a medium, like air, water, or dirt.
● EM radiation travels as a transverse wave.
Speed of EM Waves
● EM waves travel very quickly, at the speed of light – 300,000 km/s.
● EM waves reach from the sun to Earth in about 8 minutes.
● All waves in the EM spectrum travel at this speed when in a vacuum.
The Colors of Visible Light
● Different light waves have different wavelengths.
● Our eyes interpret different wavelengths as different colors.
● The longest wavelength is red.
● The shortest wavelength is violet.
● White light - what is seen when all the wavelengths get mixed in equal proportions.
● A prism – a tool used to separate the wavelengths of visible light.
Your Eyes…
● Only recognize or see 3 colors – red, green, and blue. These are called the primary colors of
light.
● All other colors we see are just a mixture of these three – this is different than what you are used
to when mixing paints.
Visible Light Spectrum
● As wavelength decreases frequency increases.
● Visible light is the part of the electromagnetic spectrum we can see and it is the smallest part of
the entire spectrum.
● ROY G. BIV - an acronym to help you remember the colors in the visible light spectrum.
● Red, Orange, Yellow, Green, Blue, Indigo, Violet - Remember, some people aren’t including
indigo in the visible light spectrum any more.
The Electromagnetic Spectrum
● Visible light is just one type of radiant energy. There is a lot of energy that travels in waves that
we can’t see.
● The Electromagnetic Spectrum – the range of frequencies possessed by electromagnetic
waves.
● Mnemonic to help you remember the order of the EM waves from longest wavelength to shortest
wavelength. Rabid Monkeys In Velvet Underpants eXcrete Goo - or make up your own!
EM Uses
● Radio – TV, radio stations, cordless phone signals, airplane communications
● Microwaves – cell phones, cook food, Doppler Radar (weather), police radar
● Infrared – TV remote control, heat treatments for illness, night vision goggles to see body
heat
● Visible Light – fiber optics, mirrors & lenses, flashlights, light bulbs, LED bulbs, lasers for
laser pointers for surgery and cutting things
● Ultraviolet – suntan, kill bacteria & viruses, detect forgery, black light to find blood and
saliva
● X-ray – see broken bones, look for hidden objects at airports
● Gamma rays – kill cancer, sterilize, smoke detectors, check for leaks in the welds of pipes,
determine the width of metal sheets, create energy in nuclear fission power plants
Too Much EM?
● The sun is the primary source of EM radiation here on Earth.
● Our atmosphere acts as a shield to most of the dangerous EM waves
● Remember:
o High frequency = more energy
o More energy = more dangerous