Refraction
1.0Master Refraction in Minutes
Demystify how light behaves when passing through different materials. Learn the governing laws of refraction, master the mathematical calculations behind the refractive index, and understand the directional shifting of light rays through clear rules and exam-focused explanations.
2.0Learning Outcomes
After completing this lesson, you will be able to:
- Define refraction of light and explain its core physical cause.
- State the Laws of Refraction and apply Snell’s Law mathematically.
- Define and calculate the absolute and relative refractive index of various media.
- Predict the directional bending of light when transitioning between optically rarer and denser media.
- Analyze everyday real-world phenomena caused by the refraction of light.
Have you ever noticed how a straight straw looks strangely bent when you place it in a glass of water? Or how a swimming pool always looks shallower than it actually is?
These everyday optical illusions are caused by a single, fundamental property of light called refraction. Whether you are preparing for a physics test or trying to understand how your eyes focus on this screen, here is everything you need to know about refraction.
3.0What is Refraction of Light?
Refraction of Light is the bending of light when it travels from one transparent medium to another due to change in speed.
In simple words: “Refraction is the change in direction of light when it passes from one medium to another.”
The amount of bending depends on:
- Nature of medium
- Speed of light
- Angle of incidence
4.0Laws of Refraction of Light
Laws of refraction state that:
- The incident ray refracted ray, and the normal to the interface of two media at the point of incidence all lie on the same plane.
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This is also known as Snell’s law of refraction.
5.0What Is the Refractive Index?
The refractive index, also called the index of refraction, describes how fast light travels through the material.
The refractive Index is dimensionless. For a given material, the refractive index is the ratio between the speed of light in a vacuum (c) and the speed of light in the medium (v). If the refractive index for a medium is represented by n, then it is given by the following formula:
Based on the refractive index of the medium, the light ray changes its direction, or it bends at the junction separating the two media. If the light ray travels from one medium to another of a higher refractive index, it bends towards the normal, else it bends away from the normal.
6.0The Rules of Refraction
How light bends depends entirely on how the speeds of the two mediums compare:
- Rule 1: Rarer to Denser Medium
When light travels from a less dense medium (like air) to a denser medium (like glass), it slows down and bends toward the normal line.
(In this case, the angle of incidence i is greater than the angle of refraction r, so i > r). - Rule 2: Denser to Rarer Medium
When light travels from a denser medium (like water) to a rarer medium (like air), it speeds up and bends away from the normal line.
(In this case, the angle of incidence is less than the angle of refraction, so i < r). - The Exception: If a light ray enters a second medium perfectly perpendicular to the boundary (at a $90^\circ$ angle, along the normal), its speed changes, but it does not bend at all. It passes straight through.
7.0Refraction of Light in Real Life
- Mirage and looming are optical illusions resulting from refraction of light.
- A swimming pool always looks shallower than it really is because the light coming from the bottom of the pool bends at the surface due to refraction of light.
- Formation of a rainbow is an example of refraction as the sun rays bend through the raindrops resulting in the rainbow.
- When white light passes through a prism it is split into its component colours – red, orange, yellow, green, blue and violet due to refraction of light.
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10.0Previous Year Question on Refraction
Question: Why does a pencil partially immersed in water appear bent?
Answer: A pencil appears bent because light rays from the submerged part undergo refraction when passing from water to air, causing the image to appear displaced.
Question: A convex lens has a focal length of 20 cm. An object is placed at a distance of 30 cm from the lens. Find the position of the image formed.
Solution: Given:
- Focal length (f) = +20 cm
- Object distance (u) = –30 cm
Using the lens formula:
1/f = 1/v – 1/u
1/20 = 1/v + 1/30
1/v = 1/20 – 1/30
1/v = (3 – 2)/60
1/v = 1/60
v = 60 cm
Answer: The image is formed 60 cm from the lens on the opposite side.
11.030second Review: Refraction of Light
- Refraction is the bending of light when it passes from one medium to another.
- It occurs due to a change in the speed of light.
- Light bends towards the normal when it enters a denser medium.
- Light bends away from the normal when it enters a rarer medium.
- The incident ray, refracted ray, and normal lie in the same plane.
- The refractive index measures the optical density of a medium.
- Refraction causes objects under water to appear raised.
- A pencil partially immersed in water appears bent due to refraction.
- Lenses work on the principle of refraction.
- Refraction is responsible for many optical phenomena such as mirages and the apparent depth of water.
12.0Recommended Next Topics