ELECTROMAGNETIC
WAVES
Nature of Waves
• A disturbance that transfers energy from one
place to another is called a wave.
• The source of any wave is a vibration.
• A substance or region through which a wave
is transmitted is called a medium.
– Mechanical waves, such as sound waves, require a
medium to travel.
Transverse Waves
• An electromagnetic wave consists of vibrating
electric and magnetic fields.
• An electromagnetic wave is a transverse wave that
transfers electrical and magnetic energy.
• Transverse waves do NOT require a medium to travel
• Unlike sound waves, electromagnetic waves can travel in a
vacuum, which means they can travel through space.
• Speed of electromagnetic waves –
– 300,000,000 meters/second
– Takes light 8 minutes to travel from the sun to earth {150
million miles} at this speed.
In order to create the vibrating
electric and magnetic fields that are
characteristic of an electromagnetic
wave, electrons must move.
How are electromagnetic waves
created?
• Electrons are arranged in energy levels.
– electrons with the lowest energy are found
closest to the nucleus
– electrons with higher energy are found farther
away from the nucleus
• If an electron moves closer to the nucleus,
energy is released & an electric and magnetic
field is created.
• These fields form electromagnetic waves.
Types of Electromagnetic Waves
Radio waves
Microwaves (a type of radio wave)
Infrared light
Visible light – red, orange, yellow, green,
blue, & violet
• Ultraviolet light (UV)
• X-rays
• Gamma rays
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Electromagnetic Spectrum
Electromagnetic Spectrum
Electromagnetic Spectrum
Radio Waves
• Have the longest wavelengths and lowest
frequencies of all the electromagnetic waves.
• Used in radios & TVs
– A radio picks up radio waves through an antenna and
converts it to sound waves.
– Each radio station in an area broadcasts at a different
frequency. # on radio dial tells frequency.
• MRI (MAGNETIC RESONACE IMAGING)
– Uses short wave radio waves with a magnet to create an
image
MRI Images
Electromagnetic Spectrum
Microwaves
• Microwaves – have the shortest wavelengths
and the highest frequency of the radio waves.
– Used in microwave ovens –
• Microwaves are absorbed by water, fats and sugars.
When they are absorbed they are converted directly
into atomic motion = heat.
• Metal reflects microwaves, which is why metal pans do
not work well in a microwave oven.
Electromagnetic Spectrum
Microwaves
• Other uses –
– Used by cell phones and pagers.
– RADAR (Radio Detection and Ranging)
• Used to find the speed of an object by sending out
radio waves and measuring the time it takes them to
return
Electromagnetic Spectrum
Infrared Rays
• Infrared = below red
– Shorter wavelength and higher frequency
than microwaves.
– You can feel the longest ones as warmth on
your skin
– Warm objects give off more heat energy than
cool objects.
Electromagnetic Spectrum
Infrared Rays
• Thermogram –a picture that shows regions
of different temperatures in the body.
– Temperatures are calculated by the amount of
infrared radiation given off.
– Therefore people give off infrared rays.
• Other uses –
– cooking - special lamps that emit thermal
infrared waves are often used in fast food
restaurants
– T.V. remote controls
Electromagnetic Spectrum
Infrared Rays
Electromagnetic Spectrum
Visible Light
• Visible spectrum – these are e/m waves we can see
• When light enters a new medium it bends
(refracts). Each wavelength bends a different
amount allowing white light to separate into it’s
various colors –
– Red, Orange, Yellow, Green, Blue, & Violet
– Longest wavelength = red light
– Shortest wavelength = violet (purple) light
LIGHT: What is it?
• Atoms – electrons release light when falling down to
lower energy levels
– photons - packets of energy released when
the electrons fall
• Light = a stream of photons, or packets of
energy, released when electrons move from
higher energy levels to lower energy levels
Electromagnetic Spectrum
Ultraviolet Light
• Shorter wavelength and higher frequency
than visible light
• Carry more energy than visible light
• Use in hospitals to kill bacteria cells – sterilization of
equipment
• Causes your skin to produce vitamin D – good for
teeth & bones (helps with the absorption of
calcium)
– Too much can cause skin cancer
• Use sun block to protect against (UV rays)
Electromagnetic Spectrum
X-Rays
Shorter wavelength and higher frequency than UV-rays
Carry a great amount of energy
Can penetrate most matter
Bones and teeth absorb x-rays. (The light part of an xray image indicates a place where the x-ray was
absorbed)
• Too much exposure can cause cancer
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– lead vest at dentist protects organs from unnecessary exposure
• Used by engineers to check for tiny cracks in structures
– The rays pass through the cracks and the cracks appear dark on film.
Electromagnetic Spectrum
Gamma Rays
• Gamma rays have the smallest wavelengths and the
most energy of any other wave in the e/m
spectrum.
– They are generated by radioactive atoms and in nuclear
explosions.
– They are also produced by such violent events as
supernova explosions (the way massive stars die).
• Gamma-rays are used to kill cancerous cells
• Gamma-rays travel to us from outer space & are
absorbed by the Earth's atmosphere.
SUMMARY
• All electromagnetic waves travel at the same
speed – 300,000,000 m/s in a vacuum
• They all have different wavelengths and
different frequencies.
– Longer wavelength  lowest frequency
– Shorter wavelength  highest frequency
– The higher the frequency the higher the energy.