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← ⚛️ Physics · usually met in Std 6-12

Light

An electromagnetic wave that also behaves like a stream of particles. It travels in straight lines until something reflects, bends or absorbs it.

A prism splits white light white light each colour bends by a different amount A rainbow is the same thing, in millions of raindrops. Refraction airwater Light bends when it changes material — which is why a straw looks broken in a glass. Light is a wave and a stream of particles. Both pictures are needed; neither alone is the whole story.
Drawn for Star Student.

Light reflects off surfaces at the angle it arrived, which is why a mirror image is predictable. It refracts — bends — when it passes between materials of different density, which is why a straw looks broken in a glass of water and why a lens can focus. A prism splits white light into colours because each colour bends by a slightly different amount, and that is also the whole explanation of a rainbow: raindrops acting as millions of tiny prisms.

Light is strange in a way that took physics a century to accept: it behaves as a wave in some experiments and as particles, photons, in others. Both are true, and neither picture alone is complete. What is not in doubt is its speed — about 300,000 kilometres per second in vacuum, the universe's speed limit, which nothing carrying information can beat.

Worth knowing

  • Sunlight takes about eight minutes to reach the Earth, so you always see the Sun as it was eight minutes ago.
  • We see only a narrow band of the electromagnetic spectrum. Radio, microwave, infrared, ultraviolet, X-rays and gamma rays are all the same phenomenon at different wavelengths.
  • The sky is blue because shorter wavelengths scatter more off air molecules, and red at sunset because the light has travelled further through the atmosphere.

Want to see it moving? Search YouTube for “Light” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.

See also

⚛️ Sound🫀 The eye⚛️ Energy

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Last gone through: 1 October 2026 · How these entries are written

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