Refraction of Light - Definition, Examples, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:34 PM IST

Have you ever seen a straw look like it is bent when it’s actually straight and inserted in a glass of water? This is because of the phenomenon known as refraction which refers to the change of direction of light as it moves from one substance to another. Refraction is the biggest contributor to the majority of the optical effects and is commonly seen in lenses glasses and in cameras.

This Story also Contains

What is Refraction?
What is Refraction of Light?
State the laws of Refraction of Light
What Causes Refraction?
Refraction of Light Examples

$Refraction of Light - Definition, Examples, FAQs$

Refraction of Light - Definition, Examples, FAQs

What is Refraction?

The change in direction of a wave traveling from one medium to another caused by its change in speed is known as refraction in Physics. In deep water, for example, waves travel faster than in shallow water. Sound waves travel faster inside of the warm air than in cold air.

What is Refraction of Light?

The ray of light bends towards normal when moving from a rarer to a denser medium, and away from normal when moving from a denser to a rarer medium.

The direction of a light ray changes when it strikes the surface separating two media this phenomenon is called as refraction. The direction of light changes as a result of this at the interface of two distinct media.

The incident light's frequency remains constant, but its speed and wavelength fluctuate. When a light beam enters a denser medium, it bends closer to the normal, whereas it shifts away from the normal in a lighter medium.

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State the laws of Refraction of Light

Refraction follows two basic laws:

Snell's law
The Angle of Refraction is dependent on the refractive indices of the two media

$refraction of light$

Snell's Law

Snell's Law provides the mathematical relationship between the angles of incidence and refraction when light passes from one medium to another.

$$
\frac{\sin \left(\theta_1\right)}{\sin \left(\theta_2\right)}=\frac{n_2}{n_1}
$$
Where:

$\theta_1$ is the angle of incidence (the angle between the incident ray and the normal)
$\theta_2$ is the angle of refraction (the angle between the refracted ray and the normal)
$n_1$ is the refractive index of the first medium (where the light is coming from)
$n_2$ is the refractive index of the second medium (where the light is entering)

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The Angle of Refraction is dependent on the refractive indices of the two media

The refractive index (denoted as n) of a material helps us to understand how much the light will slow down when it enters that material.

If a material has a high refractive index, it means light moves more slowly in that material.
If a material has a low refractive index, light moves faster in it.

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What Causes Refraction?

When a light beam is incident on the interface of two mediums, its frequency (v) remains constant. Light, on the other hand, travels at various speeds in different materials.

$$
c=v \lambda
$$

As a result, the wavelength ($\lambda$) of light at the interface varies. This, in turn, generates refraction, or a shift in direction. During refraction, it is clear that

The frequency of light does not change. The incident light deviates due to changes in light speed and wavelength.

Refraction of Light Examples

A Straw in a Glass of Water

What Happens: Try inserting a straw into a glass containing water and observe the straw looks like it has been bent at the midline in the water's surface.

Why: Light travels faster in air than in water, therefore when the light is passing from air into water (and /or from water into air), the light bends. This bending gives a glass straw the appearance of being bent at the banks of a given water body.

Seeing a Fish Underwater

What Happens: Sometimes due to reflection image of the fish may be displaced toward the surface and, therefore, appears to be closer to the observer’s eye than it actually is.

Why: When light rays are passing through one medium to another they are refracted or bent away from the normal. This bending makes the fish be seen in a position other than the real position of the fish.

Pencil Looks Like It Broke in the Water

What Happens: If you immerse a pencil into a glass of water you appear to be able to see the pencil as broken in the middle of the water's surface.

Why: Light waves slow down as they enter the water thus hitting the water's surface the pencil looks like it is bent but in a real sense it is not.

Frequently Asked Questions (FAQs)

1. Why is it so difficult to photograph a fish swimming in water?

It's tough to photograph a fish swimming in water due to light refraction.

The reason for this is that the light beams that travel from the fish to the shooter curve at the water-air boundary. As a result, the shooter only sees a picture of the fish, not the actual creature

2. Describe how a mirage form

On a hot summer day, the air directly above the road surface is extremely hot, whereas the air at higher elevations is cool.

The refractive index of air increases with density, as we all know.

As a result, the colder air towards the top has a higher refractive index than the hotter air near the road.

The hotter, thinner air goes faster than the cooler, denser air above it.

The temperature drops with height on hot days.

As a result, the refractive index of air rises with altitude.

3. What is the status of the optical fibres? What are the several applications of optical fibres in our daily lives?

An optical fibre is a very thin glass or plastic fibre with a radius of around a micrometre (10-6 m).

A light pipe is formed by a group of such tiny fibres.

4. When does a light ray at the interface of two media not deviate?

When a light ray is incident perpendicular to a surface's interface, it does not deviate.

When a light beam strikes a surface at a greater than critical angle, it does not refract but instead reflects back into the original medium.

5. When we sit around a campfire, what are the reasons for the items swaying beyond the fire?

The temperature of the surrounding air changes as a result of the campfire's heat convection.

This causes a constant change in the density and refractive index of air.

The refractive index of air changes with time, changing the refracted path of light ray

6. Can refraction occur if light travels from a denser to a less dense medium?

Yes, refraction can occur when light travels from a denser to a less dense medium. In this case, the light ray bends away from the normal line at the boundary between the two media.

7. Why does a straw appear bent when placed in a glass of water?

A straw appears bent in a glass of water due to refraction. Light rays coming from the part of the straw under water are bent as they exit the water and enter the air, causing the submerged portion to appear displaced from its actual position.

8. How does a mirage form?

A mirage forms due to the refraction of light in layers of air with different temperatures. Hot air near the ground is less dense than cooler air above it, causing light rays to bend upwards. This creates an illusion of a reflected image, often mistaken for water on a hot road.

9. Why do diamonds sparkle?

Diamonds sparkle due to their high refractive index and their cut. Light entering a diamond is bent and reflected multiple times within the stone due to total internal reflection. When the light finally exits, it's split into its component colors, creating the characteristic sparkle and fire of a diamond.

10. How does refraction affect the apparent depth of a swimming pool?

Refraction makes a swimming pool appear shallower than it actually is. Light rays from the bottom of the pool bend as they exit the water, making the bottom appear closer to the surface than it really is. This is why the pool always looks shallower than its true depth.

11. How does refraction contribute to the formation of rainbows?

Refraction plays a crucial role in rainbow formation. As sunlight enters a raindrop, it's refracted and reflected inside the drop. Different wavelengths (colors) of light are refracted by slightly different amounts, causing the light to separate into its component colors. When the light exits the raindrop, it's refracted again, creating the familiar arc of colors we see as a rainbow.

12. How does refraction contribute to the twinkling of stars?

The twinkling of stars is primarily caused by atmospheric refraction. As starlight passes through Earth's atmosphere, it encounters layers of air with different temperatures and densities. These layers refract the light slightly differently, causing rapid changes in the star's apparent position and brightness, which we perceive as twinkling.

13. How does refraction affect the color of the sky?

Refraction contributes to the blue color of the sky through a process called Rayleigh scattering. As sunlight enters Earth's atmosphere, it's scattered by air molecules. Blue light is scattered more than other colors due to its shorter wavelength. This scattered blue light reaches our eyes from all directions, making the sky appear blue.

14. How does refraction affect the apparent position of underwater objects when viewed from different angles?

The apparent position of underwater objects changes when viewed from different angles due to refraction. As the viewing angle changes, the path that light takes from the object to the observer's eye changes, altering the amount of refraction. This can make the object appear to move or change position as the observer moves.

15. What is the principle behind atmospheric refraction correction in astronomy?

Atmospheric refraction correction in astronomy accounts for the bending of light as it passes through Earth's atmosphere. As light from celestial objects enters the atmosphere at an angle, it's bent towards the normal, making the object appear higher in the sky than it actually is. Astronomers use models of atmospheric refraction to correct for this effect and determine the true positions of celestial objects.

16. What is the relationship between the angle of incidence and the angle of refraction?

The relationship between the angle of incidence and the angle of refraction is described by Snell's Law. It states that the ratio of the sines of these angles is equal to the ratio of the refractive indices of the two media.

17. What is Snell's Law and how is it used?

Snell's Law describes the relationship between the angles of incidence and refraction for light passing through a boundary between two media. It states that n₁sin(θ₁) = n₂sin(θ₂), where n₁ and n₂ are the refractive indices of the two media, and θ₁ and θ₂ are the angles of incidence and refraction respectively. This law is used to predict the path of light as it travels through different materials.

18. How does a fiber optic cable work using the principle of refraction?

Fiber optic cables work on the principle of total internal reflection. Light entering the fiber at one end is repeatedly reflected off the inner walls of the fiber, traveling along its length with minimal loss. This is possible because the core of the fiber has a higher refractive index than its cladding.

19. How does refraction affect the apparent size of objects underwater?

Refraction causes objects underwater to appear larger than they actually are. This is because light rays from the object are bent as they exit the water, making the object appear closer and thus larger. This effect is why fish often appear bigger when viewed from above the water surface.

20. How does a lens use refraction to form images?

A lens uses refraction to form images by bending light rays as they pass through it. Convex lenses converge parallel light rays to a focal point, while concave lenses diverge them. By carefully shaping the lens surfaces, we can control how light is refracted to form clear images of objects at different distances.

21. Why does light bend when it enters a different medium?

Light bends when entering a different medium because its speed changes. In a denser medium, light slows down, causing it to change direction. This change in speed and direction is what we observe as refraction.

22. What is the refractive index?

The refractive index is a measure of how much a material slows down light. It's defined as the ratio of the speed of light in vacuum to the speed of light in the material. A higher refractive index means light travels more slowly in that medium.

23. Why does a pencil appear broken when partially submerged in water?

A pencil appears broken when partially submerged in water due to refraction. Light rays from the part of the pencil under water are bent as they exit the water and enter the air. This causes the submerged portion to appear displaced from its actual position, creating the illusion of a break.

24. How does refraction affect the apparent position of stars?

Refraction affects the apparent position of stars by making them appear higher in the sky than they actually are. As light from stars passes through Earth's atmosphere, it's bent due to the changing density of air layers. This atmospheric refraction is more pronounced near the horizon.

25. Why does a fish in an aquarium appear closer to the surface than it actually is?

A fish in an aquarium appears closer to the surface due to refraction. Light rays from the fish bend as they exit the water and enter the air, making the fish appear closer to the surface than its actual position. This is similar to the effect that makes a swimming pool look shallower.

26. What is the relationship between the speed of light and refraction?

The speed of light in a medium is directly related to refraction. Light travels slower in optically denser media, which causes it to bend when entering at an angle. The refractive index of a material is defined as the ratio of the speed of light in vacuum to its speed in that material. This change in speed is what causes refraction.

27. What is the difference between real and apparent depth?

Real depth is the actual distance from the surface to the bottom of a body of water. Apparent depth is the depth perceived by an observer due to refraction. The apparent depth is always less than the real depth because light rays from the bottom are bent as they exit the water, making the bottom appear closer to the surface.

28. What is dispersion and how is it related to refraction?

Dispersion is the separation of white light into its component colors. It's closely related to refraction because different wavelengths of light are refracted by slightly different amounts when passing through a medium. This is why a prism can split white light into a rainbow of colors.

29. What is the principle behind anti-reflective coatings on glasses?

Anti-reflective coatings on glasses work by using destructive interference of light waves. A thin layer with a specific refractive index is applied to the lens surface. Light reflected from the top of this layer interferes destructively with light reflected from the lens surface, reducing overall reflection and improving light transmission.

30. How does refraction contribute to the formation of mirages in deserts?

Mirages in deserts form due to refraction in layers of air with different temperatures. Hot air near the ground is less dense than cooler air above it. Light rays from the sky are bent upwards as they pass through these layers, creating an illusion of a reflected image that looks like water on the ground.

31. What is refraction of light?

Refraction of light is the bending of light rays as they pass from one medium to another with different optical densities. This occurs due to the change in the speed of light as it travels through different materials, causing a change in its direction.

32. What is the difference between reflection and refraction?

Reflection is the bouncing back of light from a surface, where the angle of incidence equals the angle of reflection. Refraction, on the other hand, is the bending of light as it passes from one medium to another with different optical densities, causing a change in its speed and direction.

33. What is the critical angle?

The critical angle is the angle of incidence above which total internal reflection occurs. When light travels from a denser to a less dense medium, there's a specific angle at which the refracted ray would travel along the boundary between the two media. Any angle of incidence larger than this results in total internal reflection.

34. What is total internal reflection?

Total internal reflection is a phenomenon that occurs when light traveling in a denser medium strikes the boundary with a less dense medium at an angle greater than the critical angle. In this case, all light is reflected back into the denser medium, with no refraction occurring.

35. What is chromatic aberration?

Chromatic aberration is a type of distortion where a lens fails to focus all colors to the same point. It occurs because different wavelengths of light refract by slightly different amounts in a lens, causing colored fringes around the edges of images.

36. How does refraction affect the length of daylight?

Refraction extends the length of daylight by making the sun appear above the horizon even when it's physically below it. As light from the sun passes through Earth's atmosphere, it's bent downward due to refraction. This allows us to see the sun for a few minutes before it actually rises and after it has set.

37. What is the principle behind fiber optic endoscopes used in medicine?

Fiber optic endoscopes use the principle of total internal reflection. Light travels along thin optical fibers by repeatedly bouncing off the inner walls without escaping. This allows doctors to illuminate and view internal body parts by sending light through one set of fibers and receiving the reflected light through another set.

38. What is the relationship between refraction and the bending of light in optical fibers?

In optical fibers, refraction is used to confine light within the fiber core. The core has a higher refractive index than the surrounding cladding. When light hits the boundary between the core and cladding at an angle greater than the critical angle, it undergoes total internal reflection, allowing it to travel along the fiber with minimal loss.

39. What is the principle behind gradient-index (GRIN) lenses?

Gradient-index (GRIN) lenses work on the principle of continuous refraction. Instead of having a uniform refractive index, these lenses have a gradual change in refractive index from the center to the edge. This causes light to bend continuously as it passes through the lens, rather than just at the surfaces, allowing for unique optical properties and compact designs.

40. How does refraction affect the appearance of objects viewed through a curved aquarium?

Objects viewed through a curved aquarium appear distorted due to refraction. The curved surface acts like a lens, bending light rays in complex ways. This can make objects appear larger, smaller, or distorted depending on their position and the curvature of the aquarium wall.

41. What is the principle behind liquid lenses used in some cameras?

Liquid lenses use the principle of refraction at a liquid-liquid interface. By changing the curvature of the interface between two immiscible liquids with different refractive indices, the focal length of the lens can be adjusted. This allows for rapid focusing without moving parts, making them useful in compact cameras and other optical devices.

42. How does refraction contribute to the formation of halos around the sun or moon?

Halos around the sun or moon are formed by refraction of light through ice crystals in the atmosphere. Light enters the hexagonal ice crystals and is refracted twice before exiting. The specific geometry of the crystals causes light to be deflected by about 22 degrees, creating a circular halo around the light source.

43. What is the relationship between refraction and the critical angle for total internal reflection?

The critical angle for total internal reflection is directly related to the refractive indices of the two media. It's the angle of incidence above which light traveling from a denser to a less dense medium is totally reflected at the boundary. The critical angle can be calculated using Snell's Law when the angle of refraction is 90 degrees.

44. How does refraction contribute to the formation of caustics (bright patterns) in water?

Caustics, the bright patterns seen on the bottom of pools or through wine glasses, are formed by refraction. As light passes through a curved surface (like ripples on water), it's refracted at different angles. This focusing of light creates areas of higher light intensity, forming the characteristic bright, wavy patterns we observe.

45. What is the principle behind refractometers used in industry and research?

Refractometers use the principle of critical angle to measure the refractive index of substances. Light is shone through a sample onto a prism. The critical angle, where total internal reflection begins to occur, depends on the refractive index of the sample. By measuring this angle, the refractive index can be determined, which is useful for identifying substances or measuring their concentration.

46. How does refraction affect the apparent color of objects underwater?

Refraction affects the apparent color of objects underwater by altering the path of light. Water absorbs different wavelengths of light at different rates, with red light being absorbed more quickly than blue. Additionally, the refraction of light as it enters water can change the angle at which different colors reach our eyes, further altering the perceived color of underwater objects.

47. What is the relationship between refraction and the formation of optical illusions?

Many optical illusions are based on the principles of refraction. For example, the "bent pencil" illusion occurs due to the refraction of light as it passes from air to water. Similarly, mirages are caused by refraction in layers of air with different temperatures. Understanding refraction is key to explaining many visual phenomena that trick our perception.

48. How does refraction contribute to the design of corrective lenses for vision problems?

Corrective lenses use refraction to compensate for vision problems. For nearsightedness, concave lenses are used to diverge light rays before they enter the eye, allowing them to focus properly on the retina. For farsightedness, convex lenses converge light rays. The specific curvature of the lens is designed to refract light in a way that corrects the particular vision problem.

49. What is the principle behind the "disappearing glass rod" demonstration?

The "disappearing glass rod" demonstration relies on matching refractive indices. When a glass rod is immersed in a liquid with the same refractive index (often vegetable oil), light passes through both materials without bending at the interface. This makes the rod appear to vanish because there's no refraction or reflection to make it visible.

50. How does refraction affect the apparent position of the horizon?

Refraction affects the apparent position of the horizon by making it appear slightly lower than its true position. Light from the horizon is bent as it passes through the atmosphere, allowing us to see slightly beyond the geometric horizon. This effect is more pronounced over large bodies of water and can be significant for navigation and surveying.

51. What is the relationship between refraction and the formation of sun dogs (parhelia)?

Sun dogs, or parhelia, are formed by refraction of sunlight through hexagonal ice crystals in the atmosphere. Light enters the side face of a crystal and exits through another side face, being refracted in the process. This creates bright spots of light on either side of the sun, typically about 22 degrees away, often with reddish inner edges and whitish outer parts.

52. How does refraction contribute to the phenomenon of "looming" in atmospheric optics?

Looming is an optical phenomenon where distant objects appear to be elevated or magnified. It's caused by an unusual temperature inversion where a layer of warm air sits above cooler air near the ground. Light from distant objects is refracted downwards as it passes through these layers, making the objects