Refraction

Refraction of light is a very common observable phenomenon. Here we shall discuss when and where does refraction occurs in a wave, telescope, human eye, glass, etc.

The bending of a light ray as it passes from one medium to another is known as the refraction of light. Refraction occurs because the speed of a wave is different in different media. When a light wave encounters a boundary of a medium, it changes direction, speed and transforms into a wave with a different wavelength.

The refraction of light is the reason behind several phenomena in our daily life. Stars appear to twinkle in the night sky due to the refraction of light as light has to travel through several layers of air (with different densities) to reach the human eye.

The pool water appears to be less in-depth than actual depth for a person observing the pool due to refraction. Refraction is one of the reasons behind the formation of a rainbow. Optical instruments like telescopes, camera, binoculars, etc., work by the principle of refraction. The cornea in the human eye refracts most of the light as it enters our eye.

Read more about Types of Refraction: Comparative Analysis

We will explore more on this optical phenomenon and its occurrence in detail.

When does refraction occur in a wave?

A wave is a disturbance that transfers energy within a medium or from one medium to another without any transfer of particles. Refraction occurs in a wave when it is transmitted from one medium to another.

Whenever a wave encounters a different media, bending of the wave takes place. That is because; the speed of the travelling wave is different for different media. Any material, substance or space through which a wave travels is known as the medium. Refraction is not limited to light waves; it occurs in sound or water waves too. Air, water or glass are a few common examples of the medium through which light travels.

Refraction happens in all kinds of wave, like water wave or light wave. For instance a stick half immersed in water appears to be bent due to the refraction of light waves as speed of light wave is different in air and in water. Similarly, water waves move at different speed in shallow waters compared to deep waters. 

Where does wave refraction occur?

Wave refraction occurs at the boundary of the two different media through which the wave passes. Refraction is a boundary phenomenon by which any wave would behave when it encounters a new medium or any obstacle in its path.

In the case of a light wave passing through a glass prism, refraction takes place at the boundary where the light wave enters the glass prism from air or vice versa. In the case of a water wave, as it propagates over different depths the speed of the wave changes and hence the direction of propagation of the wave changes i.e., refraction takes place.

Read more about 4+ Refraction Of Waves Examples: Detailed Insight And Facts

Where in the telescope does refraction occur?

Telescope is an optical instrument that is used to view distant objects in the sky. Telescope deploys lenses to magnify smaller objects so that it is visible to the naked eye.

As the light from the distant object enters the lens of a telescope, refraction of the light wave takes place. That is because, the light from the distant object initially travelling through air enters lens, which is another medium. And as a result, the speed of light changes and hence refraction takes place. The curvature of lenses in a telescope is increased to aid for viewing the distant objects more clearly.

Read more about Telescope | 6 Important parts | Steps to use a Telescope

Where does refraction occur in the human eye?

Our vision relies on the ability of the eyes to refract light. Cornea and lens are the parts in the human eye where refraction takes place.

Most of the refraction occurs when light enters the curved clear surface of the eye called cornea. The lens also bends the light ray and aids for sharp vision. Even the tear film as well as the fluids inside our eye allows refraction for proper vision. Aqueous humor present inside our eye has a refractive index different from that of air hence the speed of light in both medium would be different.

Where does refraction occur in glass?

As we know, the speed of light is different in different media due to which each media has its own refractive index. Refractive index of glass is higher than that of air. Therefore a light ray either entering or leaving the glass medium gets refracted at the boundary separating the two media. 

For example, let us consider a light ray travelling from air to a glass slab and then through the glass slab to air, as shown in the image below.

It can be seen that the light ray bends at the region where it encounters the boundary of the glass slab. Once it enters the glass medium, it traverses through the same path until it reached the next boundary where glass meets air. The light ray suffers refraction again and finally propagates through the air.

One of the most observable instance of refraction through glass is the when we place a glass slab over a written paper. The letters appear to be magnified if we read through the glass slab. This is due to the bending of light ray as it passes through the glass slab and then to our eye.

Frequently Asked Questions

What is refractive index?

Refractive index is a measure of bending of a light ray when it travels from one medium to another. Refractive index is the property of a material.

Refractive index is the ratio of speed of light in vacuum to the speed of light in the medium. Refractive index of air (or vacuum) is unity.

Read more about Properties Of Refraction: Wave, Physical Properties, Exhaustive Facts

Also Read:

• Types of refraction
• Refraction at spherical surfaces problems
• Properties of refraction
• Uses of refraction
• What is refraction and why does it occur
• Microscope refraction index problems
• Refraction vs reflection

In this article, we will exhaustively discuss different properties of refraction, wave behavior, and its physical properties.

The following is the list of the wave and refractive index properties that we are going to discuss below:-

Wave Properties of Refraction

Snell’s Law of refraction states that “the angle of incident and the angle of refraction depends upon the refractive index of the medium” and is given by the relation as

n₁₂=n₁/n₂=Sin θ_r/ sinθ_v

The refractive index of the first medium through which the light is incident is directly proportional to the angle formed along with the normal after refraction and vice versa.

1. Speed of the wave increases in rarer medium

If the speed of the wave increases then the wave will propagate away from the normal and the refractive angle formed will be greater.

In a rarer mediums, the molecules are not closely packed and hence the light photon can travel easily without a barrier. Therefore the speed of the light ray in a rarer medium is faster as compared to a denser medium.

2. Speed of the wave decreases in a denser medium

If the speed of the wave decreases then the wave will propagate towards the normal and the refractive angle formed will be smaller.

In a denser mediums, the molecules are compactly packed, hence it becomes difficult for a light ray to penetrate through, thus decreasing its speed in denser mediums.

You can equate this while you are walking alone on the path, you can walk as fast as you can; the same is not possible when you are traveling from a crowd of people. Eventually, your speed decreases.

3. A part of the wave is reflected back

A part of the light may reflect back and leave without traversing the medium. This may be because the energy associated with the wave that reflects back is not enough to pass through the medium. The angle of incident is equal to the angle of reflection.

The same is demonstrated in the below figure.

‘I’ is the incident ray, ‘N’ is a normal axis of the object, and the angle formed by the incident ray with the normal is θ_i. ‘R’ is a reflected ray that forms a reflection angle with the normal θ_re. The incident angle and reflected angle both are equal.

The speed of the wave slightly decreases and the ray bends little towards the normal as shown in the above figure. After refraction, the light rays pass a rarer medium, and hence the speed increases and bends giving a greater angle of refraction.

Read more on Effect Of Refraction On Wavelength: How, Why, Detailed Facts.

4. The angle of refraction depends upon the density of the medium.

The speed of the wave will reduce as the wave enters the denser medium. If the speed associated with the wave is more, then the wave will deflect at a greater angle.

The ray, on refraction through the medium will propagate away from the normal if the speed of the wave increases; or will propagate towards the normal if the wave does not gain enough speed in the denser medium.

5. Amplitude of the wave decreases in a denser medium

The amplitude of wave decreases on traveling from rarer to denser medium.

Consider the below diagram, which shows the propagation of the light wave in two different mediums having a different refractive index, such that n₂>n₁.

It is indicated that the velocity of the wave is different while traversing through a medium of different refractive indexes.

As the wave travels in the medium having a higher refractive index, the amplitude of the wave becomes shorter and the velocity also decreases. On reaching back to the same medium, it regains the same amplitude and speed. Hence, the amplitude of the wave depends upon the density of the medium.

Read more on Wave Properties.

6. Amplitude of the wave increases in rarer medium

The amplitude of the wave rises on traveling from a denser to a rarer medium.

The speed of the wave is more in rarer medium, and hence the frequency of occurrence of the waves per unit time remains the same even after refraction of the wave from one medium to another.

Hence, as the speed increases, the wavelength will increases as both are correlated to each other. This implies that the amplitude of the wave increases as the speed increases that is when the wave is traveling through the rarer medium.

7. Frequency of the wave is constant

The wavelength of the wave varies but the frequency of the wave will remain unchanged on refraction.

The energy of the wave while traversing through the medium and after refraction is sustained. Hence, the frequency of the wave is constant. On entering the denser medium, the speed of the wave decreases, and the frequency of occurrence remains the same because the amplitude of the wave has decreased.

Read more on Effect Of Refraction On Frequency: How, Why Not, Detailed Facts.

8. The position at which the object appears is not the actual position.

The position of the object seems to be in accordance with the ray of light from the direction it is appearing after refracting.

On refraction, the light wave bends, and propagate in a direction making a refractive angle with the normal. Since the light ray bend at refractive angle, the observer receives rays after bending and therefore the apparent position is different from the actual position of the object.

Read more on Types Of Refraction: Comparative Analysis.

Properties of Refractive Index

The lightwave propagating from different mediums undergoes refraction and its angle of refraction and direction of propagation depends upon the refractive index of each medium.

1. Speed of the light depends upon the refractive index

The speed of the wave in the medium is based on the refractive index of the medium.

While traveling from the higher refractive index, the speed of the wave will decrease, and while traveling from the medium of a low refractive index, the speed of the wave will increase.

2. Greater the refractive index, the smaller is the refractive angle

A medium with a high refractive index will decrease the speed of the wave and hence the wave will traverse towards the normal and the refractive angle will be smaller.

3. Smaller the refractive index, the greater is the refractive angle

In a medium having a small refractive index, the wave will traverse with more speed and will propagate away from the normal, thus making a bigger angle of refraction.

4. Refractive index of a denser medium is more than the rarer medium

The speed of the wave decreases sharply in the denser medium; hence the refractive index that intensively depends upon the change in the speed of light will be more for a denser medium as compared to a rarer medium.

Read more on 16+ Uses Of Refraction: Detailed Analysis.

Frequently Asked Questions

What is the use of short wavelength beam of light in a denser medium?

A ray of a shorter wavelength travels without perturbation in the denser medium.

Since short wavelength doesn’t perturb in the denser medium, they can travel for a long distance, and hence light of shorter wavelengths are used in the denser mediums.

Why the refractive index of glass is more compared to water?

The refractive index of the medium is determined by the change in the speed of light while traveling through the medium.

The refractive index of glass is 1.5 and that of water is 1.33. The rays of light will be hindered in the solid state because of the compact molecular structure, and hence the speed will reduce as compared to the liquid state of water.

Also Read:

• Where does refraction occur
• Microscope refraction index problems
• Refraction vs reflection
• Types of refraction
• Refraction at spherical surfaces problems
• What is refraction and why does it occur
• Uses of refraction

In this article, we will discuss exhaustively about the various uses of refraction in our day-to-day life with a detailed analysis.

The refraction idea is used for different purposes in laboratories, in aquariums, auditoriums, in households and apartments, electronics and equipment, in decorative pieces, in traffic vehicles, to observe, and various others. Here is a list of some applications of the refraction:-

Telescope

Telescope has two lenses; one is the eyepiece and the objective. The objective has a large aperture and a large focal length than the eyepiece. Light from the object at a far distance is incident on the objective and the real image of the object is formed in a tube. The eyepiece then magnifies this image and produces a magnified and inverted image.

The magnifying power of the telescope is the ratio of the angle subtended at the eye and the angle subtended at the lens.

Microscope

A convergent lens of a small focal length is used to get magnified and virtual images.

The light rays are incident on the surface of the convex lens and are refracted through the lens. The image is formed behind the lens, which is larger than the real image of the object.

Magnifying Glasses

The magnifying glasses are used to see things that are difficult to read with naked eyes. Magnifiers are made up of a convex lens. The image of the object formed after refraction is an enlarged image.

Cameras

High definition (HD) cameras are in trend these days that allow us to capture minute details of the objects with a good focus of the lenses and brightness, and extraordinary photos and videos.

The camera comes with a number of lenses that define its focal length and quality of it to magnify the images and focus well on the minute objects.

Peepholes on Doors

The lens is planted on the doors of houses to peep outside through the lens to get the view of a person standing on the door. This is because of the refraction of the light through the lens.

Read more on Effect Of Refraction On Frequency: How, Why Not, Detailed Facts.

Spectacles

When the light entering through the crystalline lens of the eyes is not adjusted by the aperture of the eye lens, the image may form either behind the retina or in front of the retina, the lenses of the correct dioptre are used to correct this defect.

To Observe

A crystalline lens is present behind the cornea of our eye. This lens is biconvex and transparent and refracts the light rays entering the cornea and are focused on the retina behind the lens passes through the vitreous humor. Pupils and iris help to adjust the intensity of the light entering and the focal length of the lens.

Projectors

The projector comes with an adjustable knob to adjust the focal length of the screen while projecting a slide.

Projectors have a lens through which the beam travels and is projected on the screen. The focal length of the lens is adjusted by varying the aperture using a knob.

Periscope

A periscope uses both reflection and refraction techniques. The light enters from one lens attached to one end. The light entering from one lens is incident on the mirror kept at the middle, from where the light is reflected 90 degrees and is passed through another lens fitted on the other end of the periscope. This is used to see the objects in the obstacles, where direct sightseeing is not possible.

Binoculars

The binoculars are used to see the farthest objects. This is possible because it comes with a convex lens that produces enlarged and real images of the object. The light is refracted through the lenses of the binoculars and then receives by the eyes. The lens of the eye reads these enlarged images and processes to the brain.

Aquarium

Fish tankers and large aquarium plants use glass containers to bread fishes; to study the behavior patterns of the fishes and how they are doing in the environment that they are provided.

Read more on Effect Of Refraction On Wavelength: How, Why, Detailed Facts.

Luminance

Various laminators work on the principles of diffusion refraction. The rays of light diffuse and travels in all directions or in a straight line depending upon the structure of the laminators.

This works on the basis of refraction. The light travels through the glass and is refracted at different angles. Examples are tube lights, bulbs, LEDs, torches, lanterns, etc.

Decorative Pieces

Many decorative pieces are built using the refraction of light. For example, lanterns, glass pieces refractive white light into different components of light, crystals giving the glossy appearance, marbles, decorative pieces of glass, florescent diyas, glossy pebbles, etc.

To catch the fish swimming underwater

As the light rays travel inside the layers of the water, and then reflected back, we can see the object under the water surface.

Hence, refraction of light from the water bodies gives the view of the object underneath and we can catch the fish.

Red Light Indicator

Red light has the longest wavelength and hence disperse less in the medium and scatters least. Hence, red light is used on the vehicles during foggy weather and rainy condition so that, the vehicles approaching from a distance can be located. Red light is also used to symbolize the danger and emergency signals.

To See Eclipse

It’s difficult to look up at the sky during the daytime. During the eclipse, it is dangerous to see towards the Sun with naked eyes because of the sudden bright refraction of the rays when the moon starts revolving away opening the shield after the formation of the ring. The sudden reflection of the rays would harm the eyes.

Hence, we use different types of equipment to reduce the intensity of the light passing through our eyes. A floppy disk, black glasses, glasses painted with lamp black, etc. are used to see the eclipse by holding it across the eyes.

Read more on Types Of Refraction: Comparative Analysis.

Frequently Asked Questions

How does the refraction depend upon the emissivity of the object?

The amount of light that penetrates through the object depends relies on the refractive index of the object, that is the density.

The emissivity of the waves from the object depends on the composition, shape, and size of the object. The components of the light which are not captured by the object are refracted from the object and the same is received by our eyes.

Does the frequency of the light is constant even after refraction?

The energy of the light beam is conserved in the refraction.

The speed of the light varies on entering into the different mediums. Speed is directly proportional to the wavelength; hence the wavelength varies parallelly to the speed, keeping the frequency constant.

Why some objects are translucent?

The translucent objects are partly transparent and partly opaque.

If a few components of light are absorbed by the object and partly are refracted out, then the object appears translucent.

Also Read:

• Microscope refraction index problems
• Where does refraction occur
• Refraction at spherical surfaces problems
• Refraction vs reflection
• Types of refraction
• Properties of refraction
• What is refraction and why does it occur

In this article, we are going to discuss different types of refraction along with examples on each.

Based on the density of the medium we see various types of refractive phenomena of light. Types of refraction are listed below:-

Diffuse Refraction

When a light ray diffuses in all directions while traveling from one medium to another then it is called diffuse refraction. This effect is seen when the light ray is passed out from the concave surface and or propagates in different wavelengths and refracts at different angles.

A common example of diffusion refraction is the diffusion of light from a light bulb. The rays of the light pass in all directions, hence are used as luminance.

Specular Refraction

When a ray of light travels from one medium to another, it undergoes refraction, and a light ray bends, diverting towards or away from the normal ray, based on the refractive index of the medium.

If a light ray travels from a denser to a rarer medium, the ray of light will bend away from the normal.

The incident ray ‘i’ traveling from a medium having refractive index n₁ enters into the medium of refractive index n₂ and refracts away from the normal ray as n₁> n_2.

If a ray of light travels from a lighter to a denser medium, the ray of light will bend towards the normal.

The incident ray ‘i’ traveling from a medium of refractive index n₁ traverse through the medium of refractive index n₂ and bends towards the normal ‘N’, if n₁< n_2.

Consider a pencil inserted in a glass of water such that a part of a pencil lies immersed in the water and part of t in the air.

You will notice that a pencil appears to be slightly bent in the water. This is due to the fact that the density of water is more than the air; hence the incident rays traveling from air to the water will show some deviation from the normal ray forming an angle of refraction towards the normal.

Read more on Specular and Diffuse Reflection: Important FAQs, Concepts, Examples.

Glossy Refraction

A light ray showing both types of refraction that is diffusion as well as the specular refraction, then the surface will appear glossy. This type of refraction is called glossy refraction.

You can see glossy refraction in crystals like quartz, smoky quartz, tourmaline, amethyst, rose quartz, citrine, ruby, carnelian, etc. The light enters the crystal and is diffracted from all the faces of the crystal and is refracted specularly from one face of a crystal as shown in the below figure.

The diffusion of a light entering from the surface of the diamond gives a glossy appearance to it and the surface appears shiny.

The wavelength of the refracted light is varied from the incident light depending upon the absorption property of the material. It is clearly indicated in the above diagram that all the wavelengths of the light are absorbed in the diamonds and a wavelength in the range of 380-420nm is given out hence the crystal appears purple in color.

Some other examples of glossy refractions are water balloons, marbles, glass, LEDs, etc.

Read more on Can Light Bend Around Corners? Important FAQs.

Acoustic Refraction

The speed of a sound depends upon the density of the medium through which it travels. The speed of sound in air is 330m/s and that of water is 1480m/s.

If you have noticed the difference while you speak standing near the water bodies and normally on the ground, you can hear the person standing on the other side of a river far apart but the same is not the case when two people try to speak standing on the ground at the same distance away from each other.

Negative Refraction

When light is traveling from the medium having a negative refractive index, a ray of light is bent making an angle negative to a normal of the surface.

Consider a ray of light from a point source incident on the surface of glass slab and then converges at focus f1 and then again diverges from f1 and incident on another surface of the glass from where the rays again bend and meets normal making a negative angle.

Read more on Spherical Mirror | All Important concepts and 10+ FAQs.

Seismic Refraction

The Earth always goes under various plate tectonic activities. As the plates are floating over the asthenosphere, plates might converge or diverge depending upon the forces acting on the plate that causes its movement. The convergent or divergence of the plate arrives with different volcanic activities that cause the formation of seismic waves.

Seismic waves are categorized as primary and secondary waves. As the density of the Earth varies layer by layer, the s-waves and p-waves traveling through the Earth undergo refraction. S-wave can travel only from the solid medium whereas the p-wave which is a longitudinal wave can travel from both, solid and liquid.

Atmospheric Refraction

At a higher atmosphere, the pressure is low and hence the ray of light entering into the Earth’s atmosphere travels a longer distance. Therefore we see a shift of the objects from their actual position. Also, there is variation in the atmosphere due to temperature and pressure conditions, and air density varies. As ray travels from two different density layers, the ray of light undergoes refraction.

The atmospheric refraction is seen at night during the twinkling of the star. The position of the star appearing in the sky is not the same as they appear. The shift in the position occurs because the light ray from the star entering the Earth’s atmosphere bent due to the density difference.

The same is the case at the time of sunrise and sunset. When the sunrays hit the Earth’s atmosphere, the rays of light bend and enter through the Earth’s atmosphere, and for viewers, it appears that the Sun has already resin but in fact, the Sun is still at the horizon.

During sunset, even after the sunset, the Sun appears above the horizon due to the refraction of light receiving to the viewers.

Frequently Asked Questions

What is Snell’s Law?

The ray of light traveling from two different mediums goes under refraction.

“The ratio of the refractive angle to the incident angle is directly proportional to the refractive index of the medium from which the ray of light travels.”

Does the speed of light change on refraction?

When the light travels from one medium to another, it shows refraction.

Due to refraction, the direction of the light ray changes as it travels at different angles; hence the speed of light decreases on traveling from rarer to denser medium and further.

Why light rays do not reach the abyssal zone due to refraction?

The abyssal zone is 1500m below the surface of the ocean.

Due to the greater volume of the water, the pressure in this zone is high. The light entering from above the surface of the water diffuses and could not reach further deeper as the speed of the light reduces.

Also Read:

• Microscope refraction index problems
• Uses of refraction
• Properties of refraction
• What is refraction and why does it occur
• Refraction at spherical surfaces problems
• Where does refraction occur
• Refraction vs reflection