When a beam of light travels from one transparent medium into another—such as passing from air into water or glass—its speed changes, causing the light wave to bend. This physical phenomenon is known as refraction. Snell's Law mathematically describes this relationship, allowing physicists, lens designers, and photonics engineers to calculate exactly how much the light will bend based on the optical density (Index of Refraction) of the two materials.
Snell's Law Equation
n₁ × sin(θ₁) = n₂ × sin(θ₂)
Where n₁ and n₂ are the indices of refraction for the respective media, θ₁ is the angle of incidence, and θ₂ is the angle of refraction.
How to Use This Calculator
- Identify the missing variable you need to calculate (n₁, θ₁, n₂, or θ₂).
- Input the known Index of Refraction for the first medium (e.g., Vacuum = 1.0, Water ≈ 1.33).
- Enter the Angle of Incidence (the angle at which the light hits the boundary, measured from the normal).
- Enter the corresponding properties for the second medium.
- Click Calculate to solve the precise trigonometric relationship.
Frequently Asked Questions (FAQ)
What is the Index of Refraction (n)?
The index of refraction is a dimensionless number that describes how fast light travels through a specific material compared to the speed of light in a perfect vacuum. For example, glass has an index of about 1.5, meaning light travels 1.5 times slower in glass than it does in outer space.
What is Total Internal Reflection?
When light travels from a denser medium to a less dense medium (like from water into air), the angle of refraction is larger than the angle of incidence. If the angle of incidence is steep enough (past the "critical angle"), the light will not penetrate the boundary at all; instead, it reflects entirely back into the denser medium. This principle is how fiber optic internet cables transmit data over long distances without losing light.