Light travels at different speeds in different clear materials. When it crosses a boundary at a slant, its direction can change. Going from air into water usually bends it towards a line straight through the surface. Going straight in changes its speed but does not make its path turn sideways.
Light, sound and electricity · Discover & try
Why does light bend at a boundary?
Reading level 1 of 5 · EarlyChange
Word help
refraction
A change in light direction across a material boundary.
refractive index
A ratio describing light speed in a material.
Watch · Try · Explain
See how it works
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Flat air-to-material interface using approximate visible-light indices; reflected light is omitted.
What to look for
- The normal stays fixed
- Glass and water bend differently
- Straight entry has no sideways bend
Explain what you noticed
A ray enters glass from air at 50° from the normal. How does its transmitted angle compare?
Keep this idea: Compare direction with the normal while holding the incoming angle fixed.
Follow the sources
- OpenStax / Rice University — The Law of Refraction
- NASA / Smithsonian Chandra — Somewhere Over the Rainbow
Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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