The Physics
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Opus in profectus

Diffraction and Interference (Light)

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Discussion

obstacles and openings

Diffraction is the bending or spreading of light through an opening or around an obstacle.

Cartoon illustration of diffraction through three different sized openings and around three different sized obstacles

Goethe "flexibility of light"

Why is it possible to hear around corners, but not see around them?

double source interference

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Double source interference. Laser light through two closely spaced slits.

single source interference (self interference)

Single source interference. Laser light through a narrow opening.

Interference fringes of red laser light through a vertical slit

multiple source interference (diffraction grating)

Multiple source interference. Laser light through a diffraction grating.

Widely spaced interference fringes of red laser light through a diffraction grating

spectroscopy

continuous vs. discrete

Continuous: temperature from Wien's Displacement Law

The continuous spectrum of daylight. Note the absence of any noticeable gaps.A strip of colors with no breaks

Discrete: "bar codes" of the elements

The discrete spectrum of excited mercury vapor.
Vertical colored lines separated by black

The discrete spectrum of excited helium gas.
Vertical colored lines separated by black

The discrete spectrum of a fluorescent light. These spectral lines are wider since they came from a wider source.
Vertical colored lines separated by black. These line are wider than the previous two.

Quotes that need to be paraphrased.