How to work out refractive Index using sin i and sin r

1. Brief, precise explanation of the formula:

To find the refractive index (n) using the angles of light, you use Snell’s Law. When light passes from air into a glass block, you simply divide the sine of the angle of incidence (i) by the sine of the angle of refraction (r).

The formula is: n=sin(i)/sin(r)

Because air has a refractive index of about 1, this easy calculation shows you exactly how much the light slows down and bends when it enters the material.

AI Generated: A transparent rectangular glass block rests on paper with a pencil pointing toward its base.

Step 1: Place your glass block on a plain sheet of paper and draw a sharp outline around it with a pencil.

A diagram shows a ray box on a sheet of paper emitting a yellow light beam straight through a rectangular glass block resting on a grid.

Step 2: Shine a single ray of light (using a ray box) into the side of the block.

A physics diagram illustrates the reflection and refraction of light passing from air to glass, labeling the incident, reflected, and refracted rays alongside the normal line and the angle of incidence.

Step 3: Draw the normal line (at a 90° angle to the glass surface) where the light enters. The angle between the incoming ray and this normal line is your angle of incidence (i).

A diagram shows a red light ray hitting a rectangular glass block at an angle of incidence and bending as it passes through.

Step 4: Mark the path of the ray inside the block and as it leaves. The angle between the refracted ray inside the block and the normal line is your angle of refraction (r).

A physics diagram on a white sheet shows a light ray passing through a glass block, measured with a protractor to demonstrate refraction.

Step 5: Use a protractor to measure both angles accurately, and then calculate sin(i)/sin(r) to find your refractive index.

Snell’s Law Quick Calculator

Calculate the refractive index n instantly from your angles or sine values.

Input Mode:

Angle of Incidence (i) in degrees:

Angle of Refraction (r) in degrees:

Refractive Index (n):

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Question Snell’s Law

Snell’s Law formula

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