the electromagnetic spectrum rainbows plus a whole lot more
TRANSCRIPT
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The Electromagnetic Spectrum
Rainbows plus a whole lot more
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Wav
e vo
cab
ula
ry
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Colors of the rainbow?
Violet Blue Green Yellow Orange Red
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Describing light…
Longer wavelength Higher frequency
Higher energy
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Describing light…
Wavelength (nm)
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More than meets the eye…
Electromagnetic Spectrum
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But what is electromagnetic radiation?
• Most waves require a medium.
• EM radiation does not. They can travel in a vacuum
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• Gamma rays• X-rays• Ultraviolet• Visible• Infra-red
– “below red”
• Microwaves– Cell phones
• Radio waves
High to low energy
Ion
izin
g ra
diat
ion
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Ionizing radiation
Glossary Entry
• Subatomic particles or electromagnetic waves energetic enough to detach electrons from atoms or molecules, ionizing the atoms or molecules.
Gamma rays, X-rays, high energy ultraviolet light, alpha particles, and beta particles are examples of ionizing radiation.
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Uses for the Electromagnetic Spectrum
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Your body emits IR radiation
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Try it
Longer wavelength? Higher frequency?
Higher energy?
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Spectrum of Electromagnetic Radiation
RegionWavelength Wavelength Frequency Energy(Angstroms) (centimeters) (Hz) (eV)
Radio > 109 > 10 < 3 x 109 < 10-5
Microwave 109 to 106 10 - 0.01 3 x 109 to 3 x 1012 10-5 to 0.01
Infrared 106 to 7000 0.01 to 7 x 10-5 3 x 1012 to 4.3 x 1014 0.01 to 2
Visible 7000 to 4000 7 x 10-5 to 4 x 10-5 4.3 x 1014 to 7.5 x 1014 2 to 3
Ultraviolet 4000 to 10 4 x 10-5 to 10-7 7.5 x 1014 to 3 x 1017 3 to 103
X-Rays 10 to 0.1 10-7 to 10-9 3 x 1017 to 3 x 1019 103 to 105
Gamma Rays < 0.1 < 10-9 > 3 x 1019 > 105
Color Wavelength (nm)
Approximate energy (eV)
Violet 380-450 2.76
Blue 450-495 2.5
Green 495-570 2.2
Yellow 570-590 2.1
Orange 590-620 2.0
Red 620-750 1.65
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Energy of the rainbow
Violet Indigo Green Yellow Orange Red
2.76 eV 2.51 eV 2.2 eV 2.1 eV 2.0 eV 1.65 eV
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____ Ultraviolet
____ X-rays
____ Radio waves
____ Gamma rays
____ Visible
____ Infra-red
____ Microwaves
Try it
Rank in order of lowest to highest• Frequency• Wavelength• Energy
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Energy = Planck’s constant times frequencyE = h•ν
h = 6.62 x 10-34 Joules•second (J•s)
= 4.13 x 10-15 electron Volt•second (eV•s)
ν = frequency in Hertz (cycles/second)
Also rememberc = λ•ν c = speed of light = 3.00 x 108 m/s
So E = h • c / λ
Calculating energy
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1. Calculate the energy of a photon of infra-red radiation with a wavelength of 800 nm.
2. Your cell phone emits energy in the microwave region. Calculate the energy of a photon of cell-phone radiation with an wavelength of 10 cm.
3. The energy of a photon is measured as 4x10-19
joules . In what region of the electromagnetic spectrum does it reside? (Hint: calculate in nm)
Try it!!
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Vocabulary
Skills– Describe the electromagnetic spectrum using wavelength,
frequency or energy– Rank energies of visible light– Rank energies of electromagnetic spectrum– Convert energy wavelength, frequency energy
Concepts– EM radiation does not require a medium
• Can travel in a vacuum
– EM radiation travels in packets called photons– Higher energy EM radiation ionizes atoms or molecules
Stuff to know
wavelengthfrequencyionizing radiation
amplitudephoton