Learning path: Light

Your path

1. WavesDirect prerequisite

   A wave is a disturbance that travels from place to place, carrying energy without carrying the material along with it. Mechanical waves such as sound need a medium, while electromagnetic waves such as light can cross empty space. Every wave obeys v = fλ, and when waves overlap they add together (superposition), producing constructive and destructive interference.

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2. LightYour goal

   Light is an electromagnetic wave that travels through vacuum at exactly 299,792,458 m/s and more slowly through materials. At a boundary it reflects (angle of reflection equals angle of incidence) and refracts according to Snell's law, n₁ sin θ₁ = n₂ sin θ₂. Visible light spans roughly 400–750 nm, and it also behaves as a stream of photons, each with energy E = hf.

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Where to go next

Concepts that build directly on Light:

• Space-time: Space-time is the single four-dimensional framework of three space dimensions and one time dimension in which every event happens. Einstein's general relativity explains gravity as the curving of space-time by mass and energy, which bends the paths of light and objects and makes clocks run at different rates. These predictions have passed every test so far, from the 1919 eclipse to the GPS satellites in your phone.
• Telescopes: A telescope collects light (or other radiation) from the sky over a much larger area than the eye, letting us see fainter objects and finer detail. Its power depends mainly on the size of its main mirror or lens. Because Earth's atmosphere blurs images and blocks many wavelengths, astronomers combine giant ground-based telescopes with observatories in space such as Hubble and the James Webb Space Telescope.