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Concept · Optics
Geometric optics — total internal reflection & dispersion
critical angle sin(C)=1/n, TIR only dense→rare and at/above critical angle, prism dispersion (compare two colors' speed/wavelength/frequency/critical angle), fiber optics/mirage as TIR applications
Switches you to Physics
Named traps
12 ways this goes wrong.
Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.
- Color speed in glass reversedSays violet light travels faster than red inside glass, reversing that the higher-n violet is the slower color.→
- Color wavelength order reversedTreats violet as the longer-wavelength color and red as the shorter, reversing the visible-spectrum order.→
- Critical angle formula invertedUses sin(C)=n instead of sin(C)=1/n, or puts the larger index on top when comparing two media.→
- Critical angle from surfaceCompares the angle measured from the boundary surface to the critical angle instead of the angle from the normal.→
- Dispersion changes frequencyAttributes a prism's color spread to frequency changes in glass, when frequency is fixed and only speed and wavelength differ by color.→
- Fiber relies on mirror coatingExplains optical-fiber guiding by a reflective metal coating rather than by total internal reflection at the core-cladding boundary.→
- Higher-n color has larger critical angleAssigns the larger critical angle to the more strongly refracted (higher-n) color, reversing sin(C)=1/n.→
- Red bends most in prismClaims red light is deviated most by a prism, when violet (higher n, slower) bends the most.→
- Same critical angle for all colorsAssumes every color has the same critical angle in a given glass, ignoring that critical angle depends on each color's index.→
- TIR at any angleExpects total internal reflection at any angle of incidence, ignoring that it requires the angle to be at or above the critical angle.→
- TIR below critical anglePredicts total internal reflection for an angle smaller than the critical angle, where light still partially refracts out.→
- TIR going into denser mediumExpects total internal reflection when light passes from a less dense into a denser medium, rather than only dense to rare.→
Key formulas
No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.
Shaky underneath?
If the concept underneath still feels loose, patch it here before coming back to CSCA questions.
FoundationsPhysics 2 breadth