a walk through the electromagnetic spectrum ken morgan engr302 may 7, 2002
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A Walk Through the Electromagnetic Spectrum
Ken Morgan
ENGR302
May 7, 2002
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The Nature of Light
• Three paradigms…
– Light as an electromagnetic wave
– Light as a stream of particles (photons)
– Light as a probability wave
• Light isn’t just one of these; it’s all three!
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The Nature of Light• Light is an electromagnetic wave
In 1801, Thomas Young showed that light is a wave: Young’s double-slit interference experiment
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The Nature of Light• Light is a stream of particles called photons
The Photoelectric Effects
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The Nature of Light• Light is a probability wave
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The Nature of Light• Maxwell’s Equations
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A time-varying magnetic field is a source of a time-varying electric field.
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The Nature of Light• Maxwell’s Equations
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The sources of a magnetic field are electric currents and time-varying electric fields.
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The Nature of Light• Maxwell’s Equations
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The only source that produces a nonzero flux through a closed surface are free charges.
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The Nature of Light• Maxwell’s Equations
No analog of free charges exists for a magnetic field.
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The Nature of Light• Wave propagation
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This does not exist by itself!
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The Spectrum
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Radio• Wavelengths: ~ 100 km – 1 mm
• Frequencies: ~ 3 kHz – 300 GHz
• Energy: ~ 12 peV – 1.24 meV
Radio from space
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Radio
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Infrared• Wavelengths: ~ 1 mm – 698 nm
• Frequencies: ~ 300 GHz – 430 THz
• Energy: ~ 1.24 meV – 1.78 eV
Anything above absolute zero gives off infrared radiation.
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Visible• Wavelengths: ~ 698 nm – 400 nm
• Frequencies: ~ 430 THz – 750 THz
• Energy: ~ 1.78 eV – 3.1 eV
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Ultraviolet• Wavelengths: ~ 400 nm – 1 nm
• Frequencies: ~ 7.5x1014 Hz – 3x1017 Hz
• Energy: ~ 3.1 eV – 12.4 keV
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X-Rays• Wavelengths: ~ 30 nm – 0.03 pm
• Frequencies: ~ 1016 Hz - 1022 Hz
• Energy: ~ 40 eV – 40 MeV
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Gamma-Rays• Wavelengths: ~ 0.3 nm – 0.3 pm
• Frequencies: ~ 1018 Hz - 1021 Hz
• Energy: ~ 4 keV – 4 MeV
Gamma-ray bursts