Refraction of light. Laws of refraction

08/05/2026

The online light refraction simulations on this page will allow you to deepen your understanding of the mechanism of light refraction, its main parameters and the laws that govern it and specifically the Snell’s Law of refraction of light.

This Thematic Unit is part of our Physics collection

Angle of Refraction

Angle between the normal line and the light ray propagating through the second medium.

Apparent Depth

Visual effect caused by refraction where a submerged object appears to be closer to the surface than it actually is.

Chromatic Dispersion

Separation of white light into its constituent colors because each wavelength has a different refractive index.

Critical Angle

Limiting angle of incidence above which light no longer refracts but reflects totally within the medium.

Light Refraction

Change in direction and speed experienced by a light wave when passing obliquely from one material medium to another.

Refracted Ray

Light beam that, after passing through the separation surface between two media, continues its propagation in a different direction.

Refractive Index

Ratio of the speed of light in a vacuum to its speed in a given medium, indicating its deviation capacity.

Snell’s Law

Principle relating the refractive indices of two media to the angles of incidence and refraction of light.

What is refraction of light?

Refraction of light is an optical phenomenon that occurs when light changes direction as the medium in which it propagates changes. This change of direction occurs because the speed of light varies as it passes from one medium to another, such as from air to water or from water to glass. Refraction has applications in a variety of areas, such as fiber optics or the lens industry. Understanding the refraction of light is essential to explain and exploit a wide range of optical phenomena and technologies.

Laws of refraction of light

When light passes from one medium to another with a different propagation velocity, it undergoes a deflection in its path. The refraction of light is governed by the laws of refraction. Here are the two main laws:

First Law of Refraction

The incident ray, the refracted ray and the normal line (perpendicular to the surface) are in the same plane. The speed of light in each medium is measured by the index of refraction which is the quotient of the speed of light in vacuum and the speed of light in the medium whose index is calculated. Mathematically, it is expressed as:

n = c / v

Where:

n is the refractive index of the medium.

c is the speed of light in a vacuum.

v is the speed of light in the medium.

Second Law of Refraction. Snell’s law of refraction of light

Snell’s law of refraction of light, expresses the relationship between the angles of incidence and refraction of light as it passes through the surface of separation between two media with different index of refraction. Mathematically, it is expressed as:

n1 sinθ1 = n2 sinθ1

Where:

n1 is the velocity of light in the first medium.

θ1 is the angle of incidence in the first medium

n2 is the velocity of light in the second medium

θ2 is the angle of refraction in the second medium.

Applications of the refraction of light

The refraction of light is essential in the formation of images by lenses, such as those used in eyeglasses, cameras and microscopes. Optical lenses take advantage of the ability of light to refract to focus light to a specific point and form sharp images. The online simulations of the laws of refraction of light presented on this page will help you to understand the behavior of light and its interaction with matter.

Angle of Refraction

Angle between the normal line and the light ray propagating through the second medium.

Apparent Depth

Visual effect caused by refraction where a submerged object appears to be closer to the surface than it actually is.

Chromatic Dispersion

Separation of white light into its constituent colors because each wavelength has a different refractive index.

Critical Angle

Limiting angle of incidence above which light no longer refracts but reflects totally within the medium.

Light Refraction

Change in direction and speed experienced by a light wave when passing obliquely from one material medium to another.

Refracted Ray

Light beam that, after passing through the separation surface between two media, continues its propagation in a different direction.

Refractive Index

Ratio of the speed of light in a vacuum to its speed in a given medium, indicating its deviation capacity.

Snell’s Law

Principle relating the refractive indices of two media to the angles of incidence and refraction of light.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Light refraction simulations

Change of medium I

In this simulation you can observe the different parameters involved in the refraction of a light ray when changing medium. Observe the fulfillment of Snell’s Law of refraction of light.

Change of medium II

Prism

See what happens when you pass light through a material other than air. Try changing to different shapes and see how light behaves differently in each case. Why does white light break down into colors?

Reflection and refraction laboratory

Explore the bending of light between two media with different refractive indices. See how changing from air to water to glass changes the angle of reflection. Play with prisms of different shapes and create a rainbow. Check again how Snell’s law of refraction of light works.

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“If I have seen further, it is by standing on the shoulders of giants”

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1646

–

1716

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Michael Faraday

1791

–

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Michael Faraday discovered electromagnetic induction, conducted pioneering experiments in optics (Faraday effect), and established fundamental principles of electrochemistry.

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“Imagination is more important than knowledge”

Christiaan Huygens

1629

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1695

Christiaan Huygens developed the wave theory of light, explained double refraction, and discovered Titan, contributing to the understanding of optics and astronomy

“Light propagates as a wave advancing in all directions”

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Test your knowledge

What is the refraction of light, and why is it considered a fundamental phenomenon in optics?

Refraction is the change in direction and speed that a light wave undergoes when it passes from one material medium into another with a different refractive index. This deviation occurs only when the light strikes the boundary at an oblique angle and arises because the speed of light is not the same in all materials. Refraction is fundamental in optics because it explains how lenses work, how images are formed in optical instruments, and why we observe familiar visual effects such as the apparent displacement of submerged objects. It also reveals how light interacts with matter, since the refractive index depends on the electromagnetic properties of the medium.

How are the angle of incidence, the angle of refraction, and the refractive indices of the media related according to Snell’s law?

Snell’s law establishes a precise relationship between the angle at which light reaches the boundary and the angle at which it bends upon entering the new medium. This relationship depends on the refractive indices of the two materials, which quantify how the speed of light changes in each one. When light enters a medium where its speed decreases, the ray bends toward the normal; when it enters a medium where its speed increases, it bends away from it. This law makes it possible to predict the exact path of a light ray and forms the mathematical basis for designing lenses, prisms, and complex optical systems.

Why does light “bend” when it enters water or glass?

Light bends because its speed changes when it moves from one medium to another. In air it travels faster than in water or glass, and that change in speed forces the ray to alter its direction. It is similar to a car whose wheels enter a patch of sand at different times: the difference in speed between the sides causes the car to turn. Light behaves in an analogous way, though governed by electromagnetic interactions rather than mechanical ones.

Why does an object underwater look like it is in a different place from where it actually is?

The apparent position changes because the light reaching our eyes has been bent as it exits the water and enters the air. Our brain assumes that light always travels in straight lines, so it places the object along the extrapolated path of the refracted ray. This is why a straw in a glass appears bent or why a fish seems closer to the surface than it really is.

Do refraction and reflection happen at the same time, or are they separate phenomena?

Both phenomena can occur simultaneously. When a light ray reaches the boundary between two media, part of it may reflect back into the original medium while another part refracts and enters the new one. The proportion between reflection and refraction depends on the angle of incidence and on the optical properties of the materials. This explains why we can see reflections on the surface of water while also seeing objects beneath it.