Rainbows & Colour Separation Quiz

Concept: raindrops as tiny prisms. Water droplets refract and disperse sunlight, separating it into colours. Internal reflection and refraction on the way out send the separated colours back toward the observer.

Concept: refraction at boundaries. Light bends whenever it crosses an air–water boundary because its speed changes. A raindrop has both entry and exit boundaries, so refraction happens twice.

Concept: internal reflection in a droplet. After refraction and dispersion on entry, light reflects off the inside surface of the droplet. This reflection helps redirect the light so it can exit back toward your eyes.

Concept: rainbow formation mechanisms. Refraction bends the light at entry and exit, dispersion separates colours, and internal reflection redirects light within the droplet. Together, these processes produce the visible arc of colours.

Concept: rainbow geometry. With the sun behind you, sunlight enters droplets in front of you and can be redirected back by internal reflection. The dispersed colours then exit at angles that allow them to reach your eyes.

Concept: angular dispersion. Because refractive index depends on wavelength, each colour bends by a slightly different amount. That difference leads to different exit angles, which is why colours separate spatially.

Concept: primary rainbow colour order. Red light is deviated less than violet in water, so it exits at a slightly larger angle. That larger angle places red on the outer edge of the primary rainbow.

Concept: dispersion (n depends on wavelength). In both glass prisms and water droplets, different colours travel at different speeds, meaning different refractive indices. That makes the refraction angle colour-dependent and creates separation.

Concept: white light as a mixture. White light is made of many wavelengths in the visible range. A dispersive process can separate these wavelengths so the colours become distinct.

Concept: prism dispersion. A prism provides clear, angled surfaces that refract light strongly and separate colours. This makes the spectrum easy to observe compared with most everyday materials.

Concept: spectrum definition. A spectrum orders light according to wavelength (which corresponds to colour in the visible range). Dispersion is what spreads the wavelengths out so they can be arranged and seen.

Concept: v = c/n and normal dispersion. Greater bending corresponds to a higher refractive index, which means a lower speed in the medium. In typical glass, blue has higher n than red, so blue travels slower than red.

Concept: recombination (undoing dispersion). The second prism can bend each colour back toward the original direction by reversing the separation. If aligned correctly, the colours overlap again and appear white.

Concept: chromatic aberration from dispersion. Lenses refract different wavelengths by different amounts, so different colours focus at different positions. That mismatch produces coloured fringes, especially near edges.

Concept: chromatic aberration correction. Achromatic designs combine lenses/materials so the colour-dependent focusing errors partially cancel. That’s why a and c reduce fringes, while adding a prism or paint does not correct the underlying dispersion.

Concept: refraction vs reflection. Dispersion comes from wavelength-dependent refraction, which changes direction differently for each colour. An ideal mirror reflects without separating colours in the same way, so it doesn’t produce a spectrum like a prism.

Concept: v = fλ with constant frequency. In glass the speed of light is lower than in air, but the frequency stays fixed by the source. With v reduced and f constant, λ must decrease.

Concept: dispersion. Dispersion is specifically the separation of wavelengths because refraction depends on wavelength. It’s the reason white light can be split into a rainbow-like spread.

Concept: angular dispersion depends on geometry and n(λ). A steeper prism angle generally increases deviation and can increase separation. The material matters because stronger wavelength-dependence of refractive index produces a larger spread.

Concept: raindrops as dispersive refracting objects with internal reflection. Droplets refract and disperse sunlight, separating it into colours. Internal reflection inside the droplet sends the separated light back out toward the observer, forming the rainbow.