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Four optical effects matched to their phenomena by measurement: the aurora's line spectrum, polarized skylight, the rainbow and diffraction fringes

Four stations, four measurements: the aurora shows atomic emission lines (5), skylight is polarized by molecular scattering (4), a raindrop disperses light with a partial internal reflection (1), and a slit gives dark fringes in one colour (3) - P5, Q4, R1, S3, option A.

Sub-topics covered

• Atomic emission: lambda = hc/dE gives discrete spectral lines (aurora: O 557.7 and 630.0 nm, N2+ 427.8 nm)
• Scattering of light by molecules: the blue sky and the partial polarization of skylight, P = sin^2 theta/(1 + cos^2 theta)
• The rainbow: dispersion n(lambda) and one internal reflection in a raindrop; minimum deviation
• Single-slit diffraction: dark fringes at a sin theta = m lambda
• Total internal reflection and the critical angle

What it teaches

• The aurora is light emitted by oxygen and nitrogen excited by charged particles from the Sun: a line spectrum, not scattered sunlight
• Light scattered by air molecules is partially polarized, fully (ideally) at 90 deg from the Sun; total internal reflection reflects both polarizations fully and cannot polarize
• A rainbow needs dispersion and one internal reflection; inside the drop the ray meets the back at about 40 deg, below the critical angle 48.7 deg, so the reflection is partial, not total
• Dark and bright fringes in light of one colour behind an opening are diffraction
• P5 Q4 R1 S3: option A

Simulation ID

• ADV-2026-P1-PHY-Q14 · revision 1

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