ELECTROMAGNETIC WAVES
Dec 18, 2015
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.
• 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.
How are electromagnetic waves created?
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
Electromagnetic Spectrum
Electromagnetic Spectrum
• 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
Electromagnetic Spectrum
Radio Waves
MRI Images
• 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
Microwaves
• 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
Infrared Rays
• 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
Electromagnetic Spectrum
Visible 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
• 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 SpectrumUltraviolet Light
• 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 x-ray image indicates a place where the x-ray was absorbed)
• Too much exposure can cause cancer – 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
X-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.
Electromagnetic Spectrum
Gamma Rays
• 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.
SUMMARY