Refraction and Snell's Law
Light bends when entering a new medium: n₁ sin θ₁ = n₂ sin θ₂.
About this topic
When light passes from one medium to another its speed changes and it bends. Snell's law gives the relationship n₁ sin θ₁ = n₂ sin θ₂, where n is the refractive index. Entering a denser medium bends the ray toward the normal, and leaving bends it away.
Refraction explains why a pool looks shallower than it is, why a straw looks bent, and why lenses work. The refractive index is n = c/v: about 1.00 for air, 1.33 for water, 1.5 for glass and 2.42 for diamond. High-index materials bend light more, which gives diamonds their sparkle. Angles are always measured from the normal, never from the surface.
Worked example: a ray in air strikes water at 40 degrees. Then sin θ₂ = 1.00 × sin 40 / 1.33 = 0.643 / 1.33 = 0.483, so θ₂ ≈ 29 degrees, bent toward the normal. Going the other way, from water into air, the ray bends away and eventually can no longer escape.
Applications include glasses, cameras, microscopes, binoculars and fibre optics. Mirages come from refraction in layers of air at different temperatures. A misconception is that light bends because it changes frequency; the frequency stays the same while the speed and wavelength change. Another error is using degrees of the angle to the surface instead of the normal.
Key ideas
- Higher n means slower light
- Bends toward the normal in denser media
- Causes mirages
Quick check
Use cases: where Refraction and Snell's Law helps
- Homework: review the key idea behind Refraction and Snell's Law before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Refraction and Snell's Law without notes.
- Visual learning: play with the interactive lab to see how Refraction and Snell's Law changes when you adjust its inputs.
- Teaching a friend: explain Refraction and Snell's Law in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Refraction and Snell's Law?
Light bends when entering a new medium: n₁ sin θ₁ = n₂ sin θ₂.
What will I learn in Refraction and Snell's Law?
Higher n means slower light. Bends toward the normal in denser media. Causes mirages.
Is Refraction and Snell's Law part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Refraction and Snell's Law lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Refraction and Snell's Law?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
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