14-1 characteristics of light
1. Identify the components of the
electromagnetic spectrum.
2. Calculate the frequency or wavelength of
electromagnetic radiation
3. Recognize that light has finite speed.
4. Describe how the brightness of a light source
is affected by distance.
The Electromagnetic spectra
• Electromagnetic waves are TRANSVERSE waves which are
capable of traveling through a vacuum. Electromagnetic waves
are produced by a vibrating electric charges, they consist of
both an electric and a magnetic field at right angles to each
other.
• The alternating electric field creates alternating magnetic field,
and the alternating magnetic field creating alternating electric
field.
EM Wave Types
An EM Wave’s type depends on its frequency/wavelength
Radio
Microwave
Infrared
Visible
Ultraviolet
X-ray
Gamma Ray
103
10-2
10-5
10-7
10-8
10-10
10-12
Wavelength (m)
About the size of…
Building
Human Honey Bee Pinpoint Protozoan
Molecules
Atoms
Atomic Nuclei
Freq (Hz)
104
Temperature of
bodies emitting
the wavelength
108
1012
1K
1015
100 K 10000 K
1016
1018
10 million K
All objects emit EM radiation
1020
Visible Light Spectrum
• The visible light – the very narrow band of wavelengths in the
spectrum consists of wavelengths which range from
approximately 700 nm to approximately 400 nm. This narrow
band of visible light is affectionately known as ROYGBIV.
• Each individual wavelength within the spectrum of visible light
wavelengths is representative of a particular color.
..\..\RealPlayer Downloads\The Electromagnetic Spectrum-Visible light.flv
• All electromagnetic waves, including light, travel at the
same speed: 3 x 108 m/s in air or vacuum.
c  f 
Radio waves are electromagnetic waves. Radio waves
not sound waves
Example #1
•
1.
2.
3.
4.
Radio waves and gamma rays traveling in
space have the same
frequency
wavelength
period
speed
Example #2
•
1.
2.
3.
4.
In a vacuum, all electromagnetic waves have
the same
wavelength
frequency
speed
amplitude
Example #3
•
Compared to the speed of microwaves in a
vacuum, the speed of x-rays in a vacuum is
1. less
2. greater
3. the same
Class work – today’s date
1. Radio wave A has a wavelength of 10. meters, and
radio wave B has a wavelength of 12 meters.
Compared to the speed of radio wave A in air, radio
wave B’s speed in air is
a. lower
b. the same
c. higher
2. What is the wavelength of your favorite radio station?
3. To the nearest order of magnitude, how many times greater than
the speed of sound is the speed of light?
4. A typical microwave oven produces radiation at a frequency of
1.0x1010 hertz. What is the wavelength of this microwave
radiation?
5. The constellation of Orion is a highly recognizable arrangement
of stars. There are two very distinct stars in this constellation,
Betelgeuse which is a red star and Rigel which is a bluish star.
The color red has a wavelength of about 750 nm and the color
blue has a wavelength of about 400 nm.
a. Which color has the higher frequency?
b. Which of the two stars is hotter? Betelgeuse or Rigel?
6. An EM wave is traveling through outer space with a frequency
of 8.0 x 1013 hertz.
a. What is the wavelength of this wave?
b. What type of wave is this?
7. Listed below are the properties of several EM Waves. State
whether the property given is a wavelength or frequency, then
state which type of EM Wave it is.
a. 500000 hertz __________________ _________________
b. 5.0 x 10-9 meter _________________ _________________
c. 3.0 x 1013 hertz _____________ ____________________
d. 4.5 x 1014 hertz _________________ _________________
e. 200 meters _________________ ____________________
8. What type of electromagnetic radiation is a wave with a _____?
o wavelength of...
o frequency of…
(a) 3.5 x 103 meters
(a) 3.0 x 106 hertz
(b) 4.5 x 10-8 meters
(b) 2.2 x 1015 hertz
(c) 2.0 x 10-12 meters
(c) 1.5 x 1010 hertz
(d) 6.0 meters
(d) 5.5 x 1014 hertz
9. Electromagnetic waves can be produced by which of the following?
Which would produce a mechanical wave?
a. A plastic slinky vibrating back and forth
b. An electron oscillating back and forth
c. A neutron oscillating back and forth
d. A string with a single disturbance moving through it
e. A positively charged sphere vibrating back and forth
10. Consider the electromagnetic spectrum as you
answer these three questions.
a. Which region of the electromagnetic spectrum has
the highest frequency?
b. Which region of the electromagnetic spectrum has
the longest wavelength?
c. Which region of the electromagnetic spectrum will
travel with the fastest speed?
Huygen’s Principle
• A wave front can be
divided into point
sources.
• Each point sources
produces a circular
secondary wave, or
wavelet.
• These wavelets lines up
next to one another and
produce a new wave
front.
Ray approximation of waves
• WAVE RAY – a line perpendicular to wave’s front that shows the
direction of a wave’s travel.
λ