The Study of Light
The Electromagnetic Spectrum
 the
arrangement of electromagnetic radiation
according to wavelength.
 includes gamma rays, X-rays, ultraviolet
light, visible light, infrared radiation,
microwaves, and radio waves.
The Nature of Light
 Sometimes
light behaves like waves, and
other times like particles – it’s commonly
referred to as a wavicle.
 In the particle sense, light is thought to
consist of small packets of information,
called photons.
 In the wave sense, you can use an analogy
to waves on the ocean.
Wavelength and Frequency
• Two important terms for light are
wavelength and frequency.
Wavelength (λ)is the distance from one
wave crest to the next.
Measured in nanometers (nm)
1 nm = 1 x 10-9 m = 0.000000001 m)
Wavelength and Frequency
Frequency (f) is measured in cycles per
second = Hertz (Hz)
Number of waves that pass a given point in 1
second
Look at this animation:
http://www.ltscotland.org.uk/resources/s/sound
/amplitude.asp?strReferringChannel=resources
&strReferringPageID=tcm:4-248291-64
What is the relationship between wavelength and
frequency?
Speed of Light
 All waves in the electromagnetic spectrum
travel at the speed of light = 3 x 108 m/s.
 The speed of light is a FUNDAMENTAL
CONSTANT OF THE UNIVERSE.
 Wavelength, frequency, and the speed of
light are related by:
Speed = wavelength x frequency
Or
v = λf
Example:
• The radio station WMMR broadcasts at a
frequency of 93.3 MHz (93,300,000 Hz). How
long is one radio wave emanating from
WMMR?
– c = λf… so λ = c/f
– λ = (3.0 x 108 m/s) ∕(93,300,000 Hz)
– λ = 3.21 m
Example 2:
• Microwaves are short-length radio waves. A
typical microwave has a wavelength of 3 mm.
What is the frequency of a typical microwave?
c = λf
f = c/λ
f = (3.0 x 108 m/s) ÷ 0.003 m
f = 1.0 x 1011 Hz
Visible Light
 Visible Light is the narrow band of electromagnetic
radiation that we can see.
Visible Spectrum
 It consists of a range of
waves with various
wavelengths.
Color
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Wavelength
700 - 650 nm
649 - 580 nm
579 - 575 nm
574 - 490 nm
489 - 455 nm
454 - 425 nm
424 - 400 nm
Invisible Light
• Invisible light refers to the portions of the
EMS that humans cannot see with the unaided
eye
– Includes Radio waves, Microwaves, Infrared,
Ultraviolet, X rays, and Gamma Rays
– Radio, Micro-, and Infrared Waves all have
wavelengths LONGER than red
– UV, X and Gamma Rays all have wavelengths
SHORTER than violet
Light and Energy
• Light is actually a form of energy
• The amount of energy contained in the light is
based on the frequency of the light
– Higher frequency light has more energy
– E = hf (h = Planck’s constant = 6.6 x 10-34 Js)
Example:
• How much energy is contained in Infrared
light (f = 3 x 1014 Hz)?
E = hf
E = 6.6 x 10-34 x 3.0 x 1014
E = 1.98 x 10-19 J
How about UV light? (f = 1.0 x 1015 Hz)?
E = 6.6 x 10-34 x 1.0 x 1015
E = 6.6 x 10-19 J
Formation of Spectra
 A continuous spectrum is an uninterrupted band of
color (all the colors of the rainbow.)
 An absorption spectrum contains dark lines.
 An emission spectrum contains bright lines.
Spectroscopy
 Spectroscopy is the study of light as a function of
wavelength that has been emitted, reflected or scattered
from a solid, liquid, or gas.
 Spectrometers are in use in the laboratory, in the
field, in aircraft (looking both down at the Earth, and
up into space), and on satellites.
Types of Spectroscopy
 There are as many different types of spectroscopy as
there are energy sources! Here are just a few examples:
o Astronomical Spectroscopy
Energy from celestial objects (such as stars) is used to
analyze their chemical composition, density, temperature, and
other characteristics.
o Infrared Spectroscopy
The infrared absorption spectrum of a substance is sometimes
called its “molecular fingerprint.” Frequently used to identify
materials.
o Raman Spectroscopy
Raman scattering of light by molecules may be used to
provide information on a sample's chemical composition and
molecular structure.
Application to Earth Studies
 This is a mineral map, where each color is the
identification of specific minerals through
imaging spectroscopy analysis.
Application to Earth Studies
 The plot above shows how data from a Raman
spectrometer can be used to identify the
chemical composition of minerals.
Application to Earth Studies
 Astronomers study stellar spectra in order to
determine the chemical composition of stars.
Every star in the sky has its own unique
spectra making its identification kind of like
finger printing stars.
Electromagnetic Spectrum Song