Transcript Light and the Electromagnetic Spectrum

Dan Flavin
Untitled (Marfa Project) - 1996
The speed at which light travels through air
is approximately 300 million meters per
second.
 Light travels almost a million times faster
than sound.
 All electromagnetic waves travel at the
speed of light. Visible light is just one type of
electromagnetic wave.

› travels in straight lines at great speeds
› is reflected from mirrors in a predictable way
› Has energy in discrete packets, momentum
› Photoelectric effect
Newton observed that the reflection of light from a mirror resembles
the rebound of a steel ball from a steel plate

Thomas Young showed that light is a wave,
because it
› undergoes diffraction and interference
(Young’s double-slit experiment)
Wavelength l
 Amplitude A
 Frequency f
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Click here for video
Click here for video
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Polarization is another wave property of light.
The fact that light shows polarization tells us that
light is a transverse wave.
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The energy field
created by electricity
and magnetism can
oscillate and it
supports waves that
move.
These waves are
called
electromagnetic
waves.
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Electromagnetic waves
have both an electric part
and a magnetic part and
the two parts exchange
energy back and forth.
A 3-D view of an
electromagnetic wave
shows the electric and
magnetic portions.
http://www.walter-fendt.de/ph14e/emwave.htm
click here for video
A. Have the longest wavelengths and lowest
frequencies of all the electromagnetic waves.
 B. A radio picks up radio waves through an
antenna and converts it to sound waves.
 C. Each radio station in an area broadcasts
at a different frequency. # on radio dial tells
frequency.
 D. MRI (MAGNETIC RESONACE IMAGING)

› Uses Short wave radio waves with a magnet to
create an image
AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from
different cities.
(535kHz-1605kHz= vibrate at 535 to 1605 thousand times/second)
+
FM=Frequency modulation—waves travel in a straight line & through the ionosphere-lose reception when you travel out of range.
(88MHz-108MHz = vibrate at 88million to 108million times/second)
+

Microwaves—have the shortest wavelengths
and the highest frequency of the radio waves.
› Used in microwave ovens.
 Waves transfer energy to the water in the food causing
them to vibrate which in turn transfers energy in the
form of heat to the food.
› 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.
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Infrared= below red
Shorter wavelength and higher frequency than
microwaves.
You can feel the longest ones as warmth on
your skin
Heat lamps give off infrared waves.
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.
Shorter wavelength and higher frequency
than infrared rays.
 Electromagnetic waves we can see.
 Longest wavelength= red light
 Shortest wavelength= violet (purple) light
 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 ROYGBIV.

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The higher the frequency of the light, the higher
the energy of the wave.
Since color is related to energy, there is also a
direct relation between color, frequency, and
wavelength.
Shorter wavelength and higher frequency
than visible light
 Carry more energy than visible light
 Used to kill bacteria. (Sterilization of
equipment)
 Causes your skin to produce vitamin D
(good for teeth and bones)
 Used to treat jaundice ( in some new born
babies.
 Too much can cause skin cancer.
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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 xray was absorbed)
Too much exposure can cause cancer
› (lead vest at dentist protects organs from
unnecessary exposure)
Shorter wavelength and higher frequency
than X-rays
 Carry the greatest amount of energy and
penetrate the most.
 Used in radiation treatment to kill cancer
cells.
 Can be very harmful if not used correctly.

Animation—View a Galaxy at different
wavelengths
Brief SUMMARY
 A. All electromagnetic waves travel at
the same speed. (300,000,000
meters/second in a vacuum.
 B. They all have different wavelength and
different frequencies.

› Long wavelength-lowest frequency
› Short wavelength highest frequency
› The higher the frequency the higher the
energy.