ConceptOptics
← All conceptsGeometric 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
12 ways this goes wrong. Each one is a named misconception the questions are built to catch.
- 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.→
