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UPPCS Physics Gap Sheet: Everyday Light and Colour.
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First, the concept
Reflection returns light from a surface; refraction changes its direction when speed changes between media. Scattering redirects light in many directions. These different processes explain mirrors, bent-looking objects and the blue sky.
White light contains a continuous range of visible wavelengths. Dispersion separates colours because a material bends different wavelengths differently. Interference comes from overlapping waves and explains thin-film colours.
✅ Already asked (21)
Sky and atmosphere
- Blue sky · Air molecules scatter shorter visible wavelengths more strongly than red light.
- Red sunrise and sunset · The longer atmospheric path removes much short-wavelength light from the direct beam.
- Red danger signals · Red light has a long visible wavelength and is scattered less by small particles.
- Black sky in space · Without a substantial atmosphere, sunlight is not scattered across the sky.
- Sun near the horizon · Unequal refraction of rays from its lower and upper edges makes it look flattened.
- Mirage · Light curves through air layers at different temperatures; the school-level explanation includes total internal reflection.
Colour and wave effects
- Rainbow colour order · A primary rainbow has red on its outer edge and violet on its inner edge.
- Prism dispersion · In ordinary glass, violet deviates more than red.
- Soap-film colours · Reflections from the film's two surfaces interfere.
- Oil-film colours · Thin-film interference produces changing colours on water.
- Green grass · Grass reflects green light more strongly than many other visible colours.
- Green filter under red light · An ideal green filter appears dark because it transmits little red light.
- Hot-star colour · Blue stars generally have higher surface temperatures than red stars.
- Diffraction · Light spreads around edges and narrow openings, especially when their size approaches its wavelength.
Refraction and reflection
- Bent-looking rod in water · Refraction changes the apparent position of its submerged part.
- Frequency at a boundary · Frequency stays unchanged when light enters another stationary medium; speed and wavelength change.
- Diamond brilliance · Its high refractive index favours repeated total internal reflection.
- Optical fibre guidance · Light is guided by total internal reflection when core and cladding conditions are suitable.
- Albedo · The fraction of incoming radiation reflected by a surface; fresh snow has high albedo.
- Sunlight travel time · Sunlight reaches Earth in about 8 minutes 20 seconds.
- Stroboscopic effect · Intermittent illumination can make moving objects look still or appear in several positions.
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🔒 10 items not asked yet
Sky and atmosphere: 2 · Refraction and reflection: 1 · Further optical effects: 7
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⚠️ The sky is blue mainly from scattering; soap-film colours come from interference. A rainbow needs refraction, dispersion and internal reflection.
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