Dispersion Basics Explained: Prisms, Rainbows, Colours

Concept: dispersion (wavelength-dependent refraction). Different wavelengths experience different refractive indices in a material, so they bend by different amounts. This unequal bending spreads white light into its component colours.

Concept: prism dispersion. A prism refracts light at its surfaces, and the refractive index depends on wavelength. Because each colour bends differently, the outgoing beam separates into a spectrum.

Concept: refraction + dispersion in droplets. Sunlight entering a droplet refracts and disperses, separating colours. The light also reflects inside the droplet and refracts again as it exits, sending separated colours toward your eyes.

Concept: spectrum. A spectrum is the ordered spread of light by wavelength (or colour). Dispersion is the process that produces this spread from white light.

Concept: normal dispersion. In typical glass, shorter wavelengths (blue/violet) have a slightly higher refractive index. A higher refractive index means stronger bending toward the normal, so blue/violet refract more.

Concept: refractive index as a function of wavelength, n(λ). Different wavelengths travel at different speeds in the same material. Since refraction depends on speed (or n), the bending becomes colour-dependent.

Concept: v = c/n (speed depends on refractive index). Blue light often has a slightly larger refractive index in glass, so it travels slightly slower. Red light has a slightly smaller refractive index, so it travels slightly faster.

Concept: dispersion in water droplets. Raindrops act like tiny prisms that separate sunlight into colours. The combined effect from many droplets produces the visible rainbow.

Concept: frequency continuity at a boundary. When light enters a new medium, its frequency is set by the source and stays the same across the boundary. The speed and wavelength change instead, and the colour separation comes from wavelength-dependent refraction.

Concept: white light as a spectrum of wavelengths. White light contains many visible wavelengths combined together. Dispersion separates these wavelengths so you can see the individual colours.

Concept: wave relation v = fλ. If the speed v decreases while frequency f stays constant, the wavelength λ must decrease. This is why light has a shorter wavelength inside a higher-index medium.

Concept: wavelength-dependent refraction. A prism refracts each colour by a different amount because n varies with wavelength. The prism’s geometry then turns that difference into visible angular separation.

Concept: reversibility of refraction (undoing dispersion). A second prism oriented appropriately can bend each colour back toward the others. If the angles match, the separated spectrum recombines into white light.

Concept: spectroscopy via dispersion. A spectroscope spreads light into a spectrum so different wavelengths can be seen or measured. This separation is produced by dispersion (or by a grating using a different mechanism).

Concept: dispersion as n(λ)-driven refraction. Different colours bend differently because each wavelength experiences a different refractive index. That wavelength-dependent bending can split white light into a spectrum, so a, c, and d are correct.

Concept: primary rainbow geometry + dispersion. Red light exits droplets at a slightly larger angle than violet, so it forms the outer edge of the arc. Violet is more deviated and appears on the inner edge.

Concept: strength of dispersion depends on Δn across wavelengths. If n(λ) varies strongly, different colours experience larger differences in bending. That increases the angular separation, making dispersion more noticeable.

Concept: more bending → higher refractive index (in normal dispersion). Greater refraction toward the normal corresponds to slower speed in the medium. Since v = c/n, slower speed means larger n, so violet has higher refractive index than red.

Concept: angular dispersion. Because each wavelength refracts by a different amount, each colour exits in a different direction. The result is a fan-like spread of colours at different angles.

Concept: dispersion (wavelength-dependent refraction). Dispersion happens when different wavelengths experience different refractive indices and therefore bend by different amounts. This is why prisms and raindrops can split white light into colours.