EC-5.1 Waves, Interference and Optics
You can describe a wave by its amplitude, frequency, wavelength and phase, predict what two waves do when they meet, and say what happens at a boundary between two media.
Before:nothing requiredUnlocks:PE2-5. MEMSEC-6. Semiconductor Devices and Device Models
Wave behaviour is one of the few pieces of physics that reappears in almost every later subject here, and each of those subjects re-derives it badly. A signal on a line, light in a fibre, a field crossing an interface and an electron in a crystal are all the same mathematics wearing different units. Meeting it once, on its own, means the electromagnetics course can spend its time on fields rather than on what a wave is, and the fibre-optics option can start at the fibre.
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The four numbers that describe any wave, and how they relate
Amplitude, frequency, wavelength and phase are enough to write down a travelling wave completely, and the speed ties frequency and wavelength together. Getting comfortable moving between period and frequency, and between wavelength and wavenumber, removes most later arithmetic errors.
NPTEL: Wave Optics · CourseSuperposition, and what two waves do where they overlap
Waves add rather than collide, so two arriving in step reinforce and two arriving opposed cancel. Everything called interference is that one statement applied to a particular geometry.
Path difference, and why a small distance changes the answer completely
Whether two waves arrive in step depends on the difference in the distance each travelled, measured in wavelengths. A shift of half a wavelength turns full reinforcement into full cancellation, which is why optical measurements can resolve distances far smaller than any ruler.
MIT OpenCourseWare 8.03SC: Physics III — Vibrations and Waves · CourseDiffraction, and why a wave will not stay in a straight line
A wave passing an edge or through an opening spreads, and it spreads more when the opening is comparable to the wavelength. This is the reason an antenna has a beam width and a lens has a resolution limit.
Refraction and reflection at a boundary between two media
At an interface, part of the wave crosses with its direction bent and part comes back, in proportions set by the two media. Total internal reflection above a critical angle is the same result taken to its limit, and it is what makes an optical fibre possible.
NPTEL: Wave Optics · CoursePolarisation, and what it means for a wave to have an orientation
A transverse wave oscillates across its direction of travel, so it also has an orientation, which can be fixed, rotating or random. Filters, antennas and liquid-crystal displays all work by selecting one orientation over another.
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