Snell’s Law
Refraction of light uses sines of angles.
Key idea
Refraction of light uses sines of angles.
In depth
n₁ sin θ₁ = n₂ sin θ₂ relates the angles of light passing between media with refractive indices n₁ and n₂. Light bends toward the normal when entering a denser medium. It follows from light taking the quickest path.
Worked example
Air (1.00) to water (1.33) at 45°: sin θ₂ = 0.707/1.33 = 0.532, θ₂ ≈ 32.1°.
Formula
Real-world uses
- Designing eyeglasses, camera lenses and fibre-optic cables that bend light correctly
Common mistake
Measuring angles from the surface instead of the normal.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Snell’s Law?
Refraction of light uses sines of angles. It is a topic at the expert level in Trigonometry.
What is the formula for Snell’s Law?
The key formula is n₁ sinθ₁ = n₂ sinθ₂.
Where is Snell’s Law used in real life?
Real-world examples: Designing eyeglasses, camera lenses and fibre-optic cables that bend light correctly.
What should I learn before Snell’s Law?
Make sure you are comfortable with Trigonometry in Physics, the previous topic in Trigonometry.
What is a common mistake with Snell’s Law?
Measuring angles from the surface instead of the normal.
How can I practise Snell’s Law?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Snell’s Law?
Move on to Range of a Projectile next.
Related expert topics in Trigonometry
- Half Angle Formulas – Trig of θ/2.
- Power Reducing Formulas – Reduce squares to first powers of cos 2θ.
- Product-to-Sum Formulas – Convert products into sums.
- Sum-to-Product Formulas – Convert sums into products.
- Triple Angle Formulas – sin3θ and cos3θ in terms of θ.
- Trig and Inverse Trig Compositions – Evaluate expressions like sin(arccos x).