The Electromagnetic Spectrum

Rainbows plus a whole lot more

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Colors of the rainbow?

Violet Blue Green Yellow Orange Red

Describing light…

Longer wavelength Higher frequency

Higher energy

Describing light…

Wavelength (nm)

More than meets the eye…

Electromagnetic Spectrum

But what is electromagnetic radiation?

• Most waves require a medium.

• EM radiation does not. They can travel in a vacuum

• Gamma rays• X-rays• Ultraviolet• Visible• Infra-red

– “below red”

• Microwaves– Cell phones

• Radio waves

High to low energy

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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.

Uses for the Electromagnetic Spectrum

Your body emits IR radiation

Try it

Longer wavelength? Higher frequency?

Higher energy?

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

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

____ Ultraviolet

____ X-rays

____ Radio waves

____ Gamma rays

____ Visible

____ Infra-red

____ Microwaves

Try it

Rank in order of lowest to highest• Frequency• Wavelength• Energy

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

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!!

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