A Walk Through the Electromagnetic Spectrum Ken Morgan ENGR302 May 7, 2002

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!

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

The Nature of Light Light is a stream of particles called photons The Photoelectric Effects

The Nature of Light Light is a probability wave

The Nature of Light Maxwell’s Equations A time-varying magnetic field is a source of a time-varying electric field. or

The Nature of Light Maxwell’s Equations or The sources of a magnetic field are electric currents and time-varying electric fields.

The Nature of Light Maxwell’s Equations or The only source that produces a nonzero flux through a closed surface are free charges.

The Nature of Light Maxwell’s Equations No analog of free charges exists for a magnetic field. or

The Nature of Light Wave propagation This does not exist by itself!

The Spectrum

Radio Wavelengths: ~ 100 km – 1 mm Frequencies: ~ 3 kHz – 300 GHz Energy: ~ 12 peV – 1.24 meV Radio from space

Radio

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.

Visible Wavelengths: ~ 698 nm – 400 nm Frequencies: ~ 430 THz – 750 THz Energy: ~ 1.78 eV – 3.1 eV

Ultraviolet Wavelengths: ~ 400 nm – 1 nm Frequencies: ~ 7.5x10 14 Hz – 3x10 17 Hz Energy: ~ 3.1 eV – 12.4 keV

X-Rays Wavelengths: ~ 30 nm – 0.03 pm Frequencies: ~ Hz Hz Energy: ~ 40 eV – 40 MeV

Gamma-Rays Wavelengths: ~ 0.3 nm – 0.3 pm Frequencies: ~ Hz Hz Energy: ~ 4 keV – 4 MeV Gamma-ray bursts