Snell's law
Intermediate
Law of refraction.
refractionn₁ sinθ₁ = n₂ sinθ₂ relates the angles in two media, measured from the normal. It follows from Fermat's principle.
Air to glass at 40°: θ₂ = 25.4°.
Check the angles in the correct order.
In more detail
Snell's law states that n1 sin θ1 = n2 sin θ2, relating the angles of incidence and refraction to the refractive indices. It describes the bending of light at a boundary.
Real-world uses
- Designers of lenses and fibres use Snell's law.
- Geophysicists use it to model seismic refraction.
- Opticians use Snell's law to design glasses, and marine biologists use it to explain how fish see the sky.
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Frequently asked questions
What happens at normal incidence?
Light passes straight through without bending.
Who discovered it?
Willebrord Snell, though it was known earlier in other forms.
What is the rule in words?
Light bends toward the normal when entering a denser medium, and away from it when entering a less dense one.
Related topics in Optics
Focal length and radius · Refraction of light · Refractive index · Apparent depth · Critical angle · Total internal reflection