What is Light, and How is it Generated?

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 What is Light, and How is it Generated? is the second lecture within the Waves and Optics section of PH1011. It gives a further understanding as to the nature of light.

Particle vs Wave
Light travels by means of carrier particles - photons - which have properties reminiscent of both particles and waves. This wave particle duality is present in the fact that light can be observed diffusing and spreading like a wave, but can be detected as individual quantised energy sets (E = hf) and during the photoelectric effect acts as a particle through emission only being possible above certain threshold frequencies. It nonetheless displays a distinct wavelength and frequency, as waves do.

Black body radiation and Atomic Emission
All bodies emit radiation on principle; a "black body" is defined as a perfect radiator, which therefore emits the widest range of EM radiation. This is caused by the vibration of electrons - atomically photons can also be released as electrons undergo energy level transitions, moving to lower energy levels and releasing specific wavelengths of light with energies corresponding to the difference in levels.

The colours of light experienced through vision are dependent entirely on the wavelengths of the light source rather than properties of objects - if a blue lamp is shone onto an object which appears red in white light the object will appear black as it absorbs blue and green light but reflects red - and in this case there is no red to reflect.

Summary
Electromagnetic radiation displays wave-particle duality. It can be radiated from black bodies or emitted from atomic shifts in electron orbitals.