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Electromagnetic Waves
What are they?
UCSD: Physics 8; 2006 3Spring 2006
Examples of Electromagnetic Waves/Radiation
• Radio Waves (AM and FM radio waves andTV signals)
• Cell phone communication links• Microwaves• Infrared radiation• Light • X-rays• Gamma rays• What distinguishes these from one another?
Electromagnetic Waves are
waves of electrical and magnetic energy with different wavelengths
and frequencies..
Speed of electromagnetic waves = 300,000,000 meters/second (Takes LIGHT 8 minutes to travel from Sun to Earth at this speed!!)
•Electromagnetic (EM) Waves need NO MEDIUM (matter) to travel.
•They are TRANSVERSE waves that travel through EMPTY SPACE!!
•However, they can travel through a medium (matter).
EM waves travel as VIBRATIONS in ELECTRICAL and MAGNETIC FIELDS
Electromagnetic waves are arranged from longest to shortest wavelength forming the Electromagnetic Spectrum.
The Longer the wavelength, the Lower the frequency = Low energy. (Rule of Ls)
The sHorter the wavelength, the Higher the frequency = High energy. (Rule of Hs)
That this set of waves passed by a point in one second. There are 5 waves in this picture. The frequency of this wave is therefore 5 cycles per second (Hz).
This set of waves passed by the same point in one second. There are 13 waves in this picture. The frequency of this wave is therefore 13 cycles per second (Hz).
Low Frequency
High Frequency
Radio Waves
• Radio waves have the Longest wavelengths and Lowest Frequencies of all the electromagnetic waves.
• A radio picks up radio waves through an antenna and converts it to sound waves.
Radio waves are divided into:-
FM, Frequency modulation.
AM, Amplitude modulation
VHF, which stands for "Very High Frequency“. This is where you find stereo "FM" radio stations. Further up the VHF band are civilian aircraft and taxis.
UHF stands for "Ultra High Frequency”. It's used for Police radio communications, television transmissions and military aircraft radios.
•Radio waves are made by various types of transmitters, depending on the wavelength.
•They are also given off by stars, sparks and lightning, which is why you hear interference on your radio in a thunderstorm.
Microwaves
• Microwaves are a type of radio wave. They have the shortest wavelength and the highest frequency of the radio waves.
• Microwave ovens transfer energy to the water in the food causing them to vibrate.
• Microwaves are also used by cell phones and pagers!
A. Radar Radar (radio detection and ranging) devices
send out short pulses of microwaves, count the time until they return, and then calculate the distance to an object.
Radar is used to monitor airplanes, ships, and to track weather systems. Police use radar guns to calculate the speed of drivers.
Infrared Rays
• Heat Lamps give off infrared waves and so do living things!!
• You can feel the longest waves as warmth on your skin!
• Used in remote controls
Infrared Lie-detection
Before the lie After the lie
The military uses IR to see objects it considers relevant
IR light penetrates fog and smoke better than visible light.
Visible Light• The only EM waves
our eyes see every day.
ROYGBIV
Ultraviolet Rays
• Used to kill bacteria and sterilize equipment!
• Causes skin to produce vitamin D, good for teeth and bones!!
• Too much can cause SKIN CANCER!!! • Used to treat jaundice in new born
babies
X-RAYS
• Great amounts of energy, can penetrate through most matter!
• Bones and teeth Absorb x-rays, that is how we see them in the x-ray picture.
• Too much can cause cancer!!
Gamma Rays
• Carry greatest amount of energy and can penetrate through most matter!!
• Used in radiation treatment to kill cancer cells.
• Very harmful if not used correctly!!!
Sources of EM waves
How the EM Spectrum Helps us Judge Distances in Space:
Because the Universe is so Vast, interstellar distances are so great that the light emitted from other objects in space can take upwards of millions of years to reach us!!!So how can we tell just how far away an object is??????
Distances are measured in Light Years – this is how far light travels through space in 1 year (about 6,000,000,000,000 miles).Because it takes so long for light to travel through space, the light arriving at us would have actually left the object many years ago.
Looking at a far away star is like looking back in time!!!
So, we use specific types of telescopes and satellites out in space to take pictures of the EM waves and scientists can then determine what type they are, then judge how many light years away the object is!
But still, how does this help us see objects in space? Well…
Extremely smart scientists have figured out that different types of ElectroMagnetic waves travel through our atmosphere at different frequencies and wavelengths.
Scientists can determine where an object is located by the type of EM wave emitting through our atmosphere!!
