CBSE Class 10: All You Should Know About Refraction of Light

Have you ever wondered how light travels inside different mediums? Well, we know that light is a form of energy and can undergo various natural phenomena like reflection, diffraction, refraction, polarization, and interference. Today we will be learning about refraction, which is a phenomenon that takes place due to the natural bending of light. But first of all, let us have a brief explanation of what it actually is!

What is the Refraction of Light?

In simple terms, refraction is the bending array of light when it passes from one medium to another. The medium can be water, sound, or any other transparent medium.

All factors that are responsible for the bending of light are caused due to the difference in the density between the two mediums.

It is interesting to know that due to this refraction of light, we are able to see things across magnifying glasses, lenses, prisms, etc. The focus of our eyes relies upon the refraction of light.

Definition of Refraction

Refraction is the change in the direction of a wave passing from one medium to another.

Curiously enough: Do you know that the twinkling of the stars is due to atmospheric refraction? Yes, the light coming from the stars goes through different levels of refraction until they reach the earth.

Here is a blog that gives some expert tips on how to prepare for CBSE Exams.

What are the Key Features of Refraction?

• Refraction plays a vital role in forming the image of an object in the lens and other transparent mediums.
• The speed of light, as well as the wavelength, are reduced in slower mediums.
• The refractive index talks about the ratio between the speed of light in a medium and the speed of light in a vacuum.

What are the Causes of Refraction?

Even though refraction is a natural phenomenon, there are certain causes that lead to it. 

• The refraction of light Happens when a ray of light travels at an angle into a different medium with a different refractive index.
• Refraction takes place when the intensity of a refracted ray is less than an incident ray.
• A ray of light is refracted when the deviation of the part of light takes place. Thus, changing the wavelength and speed of light.
• For example, when light passes from air into glass, the light slows down and changes its direction. It is because when light travels from a medium of less density to a medium that is denser, the refracted light tends to bend towards the normal line.

Have you ever wondered how certain materials look magnified when they enter the water? Well, the answer is plain and clear. It is because of the refraction of light.

Types of Refraction

• Refraction from denser to the rarer medium

In this case, light travels from a denser medium to a rarer medium. For example, when it passes through glass to air. Here, the refractive index is less than one.

• Refraction from rarer to the denser medium

In this case, light travels from a rarer medium to a denser medium. For example, when it passes from air to glass. Here, the refractive index is greater than one.

Laws of Refraction of Light

Now that we have a well-detailed idea about the phenomenon of refraction, let us now understand the two important laws about the same.

Laws of reflection state that-

• The reflected ray, the incident ray and the normal to the interface of the two media at the point of incidence all lie on the same plane.
• The ratio of the sine of the angle of refraction to the sine of the angle of incidence is constant. This is also known as Snell’s law of refraction.

Sin i/ Sin r = Constant

What is Snell’s Law?

Snell’s law is an essential component to effectively understand the refraction of light. This law gives the angle of the bending ray of light on the indices of refraction of two media.

What is a Refractive Index?

The refractive index, also called the index of refraction, describes how fast light travels through the material.

The refractive index is a ratio between two entities, and it is dimensionless. For a given material, the index of refraction 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 is represented by n, then the resulting formula would be-

n = c/v

Based on the observations of the refractive index of a medium, it is noticed that the ray of light changes its direction or bends at the junction separating the two media.

It is seen that if the light ray travels to a medium of higher refractive index, it tends to bend towards the normal or else it bends away from the normal. 

Have you ever observed how nature pays with the laws of refraction? Keep reading to learn about the most common incidents that go out of our notice.

Also See: What is Light Made Of  | Wavelength of Light  |  Reflection of Light

Effects and Examples of Refraction of Light in Real Life

Refraction is an important phenomenon that can be witnessed in terms of optics and technology. The most common examples that explain refraction that we see in our daily lives are-

• Various optical illusions happen because of the phenomena of refraction of light.
• The twinkling of the stars is caused due to the refraction of light.
• It is due to the refraction of light that a swimming pool always looks shallower than it really is.
• The formation of a rainbow is a major example of the refraction of the light rays coming from the sun.
• When a ray of white light passes through a prism, it splits into its significant colours. It happens due to the refraction of light.

Applications of Refraction of Light

The phenomenon of refraction of light is applicable in various branches of optics and technology. Let us know a few of the known applications of refraction of light.

• The laws of refraction are used for the lens in order to form a magnified image.
• The spectacle lenses used by visually defective individuals use the laws of refraction to form the right image.
• The series of colours- VIBGYOR, that we see after a white light passes through a prism is the result of light refraction.
• Equipment like cameras, telescopes, and movie projectors uses the principles of refraction.

Some Solved Problems on Refraction of Light

1. A ray of light enters into a medium of refractive index 1.44.

a) What is the direction of the bending of the light?

b) The angle of incidence on one end of the fiber happens to be 22°, then what will be the angle of refraction?

Solution:

a) As the light rays travel from a rarer medium to a denser medium, the refracted ray will bend towards the normal.

b) The angle of refraction is calculated as follows:

Let air be medium 1 and the optical fibre is medium 2.

So,

n₁ = 1.00

n₂ = 1.44

and θ₁= 22°

Now, substituting the above-mentioned values in the equation results as follows:

(1.00) sin 22° = 1.44 sin θ₂.

sin θ₂ = (1.00/1.44) sin 22° = 0.260

θ₂ = sin^-1 (0.260) = 15°

2. In an optical fibre, a ray of light passes through it and reaches its end, and passes out into the air. Suppose the incident angle at the end of the optical fibre tube is 30°. Then, what would be the refractive angle outside the fiber?

Solution:

Let the fibre be medium 1 and air medium 2.

Therefore,

n₁ = 1.44

n₂ = 1.00

and θ₁ = 30°. 

Substituting the above information in the equation below, we get,

(1.44) sin 30° = 1.00 sin θ₂

sin θ₂ = (1.44/1.00) sin 30°

= 1.44 (0.500)

= 0.720

And, θ₂ = sin^-1 (0.720)

= 46°

This time we observe that the refractive angle is larger than the angle of incidence. This calculation indicates that the light is bending away from the normal as it enters a rarer material.

Practice Questions After understanding the laws of refraction of light, it is now time to solve the questions below- The rays of light travel through an optical fibre. The light reaches the end of the tube and then exits into the air. If the angle of incidence formed at the end of the fibre tube is 45°, then what will be the angle of refraction formed outside the fibre? A light passing in the air enters an optical fibre with a refractive index of 1.44. In which way the beam of light will bend? The angle of refraction at the other end of the tube is calculated to be 30°. What will be the angle of incidence? A concave lens has a focal length of 20 cm. At how much distance from the lens a 5 cm tall object can be placed so that it forms an image right at 15 cm from the lens? Also, what will be the size of the image formed? An object which is 50 cm tall is placed on the principal axis of a convex lens. Suppose a 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens. If a light ray is an incident on the surface AB as shown, identify the correct emergent ray.‘The refractive index of diamond is calculated to be 2.42.’ What is the meaning of this statement in relation to the speed of light?

Frequently Asked Questions About Refraction of Light