Transcript The Electro-Magnetic Spectrum - EHS

The Electro-Magnetic
Spectrum
Light Properties

Have properties of waves…
•Crests & troughs
•Reflect & refract (bend)

…and particles
•Can travel through space
EM Waves
The Speed of Light = c
= 3 x 108 m/s (1.9 miles/second)
 Travels around the world about 8 times in
one second
c=
 = frequency &  = wavelength
 Frequency = Hertz (Hz)=1/ second
Wavelength is a length – m to nm

EM Spectrum
Spectrum means “a range”
 EM spectrum ranges from long
wavelengths to short

Wavelength and Frequency
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www.nasa.go
Wavelength is the distance
between two peaks (or
troughs)
Frequency is how frequently
the waves occur
A longer wavelength means a
lower frequency
A shorter wavelength means a
higher frequency
Energy
Frequency


As frequency
decreases, energy
increases
E = h
• h = 6.626 x 10-34
Joules *second

Higher energy =
high frequency =
short wavelength!!
Energ
y
Light as a Particle
Light = photons
 Photons are considered to be
both particle and a wave
 What does that mean?

• A photon is a “wave packet”
• A photon is a “light particle”
The Visible Spectrum
red
620-750 nm
orange
590-620 nm
yellow
570-590 nm
green
495-570 nm
blue
450-495 nm
indigo
420-450 nm
violet
380-420 nm
Visible Light
Not all animals see the same
wavelengths as humans
 Some see shorter wavelengths
(ultraviolet)

• Hummingbirds
• Bees

Others see longer wavelengths
(infrared)
• Bats
• Snakes
Visible Light vs. UV
Flower in visible
light
Flower in UV
light
Visible Light vs. Infrared
Bats in
infrared light
Bats in
visible light
Full Visible Spectrum
Red
Orange
Yellow
Green
Blue Violet
(Indigo)
What does this have
to do with
Astronomy??
Two Girls in the IR
Is this in “true color?”
http://en.wikipedia.org/wiki/Infrared
How do we know what a
star is made of??
By looking at its EM spectrum
 The star’s “fingerprint”

Hydrogen
How light or electromagnetic
radiation is used in Astronomy
• Astronomers use spectroscopes
• separate starlight into its colors
• Identify star’s composition,
temperature, luminosity
• Different wavelengths provide
different information
• Temperature – Blackbody Radiation
• Composition – Absorption Spectrum
• Luminosity/Brightness
Emission Spectra
Full
spectrum
Wavelengths:
H
Models of a Hydrogen
Atom
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PhET's Model of a Hydrogen Atom