Class 10 Light – Reflection and Refraction Study Notes

Light is the most important source of energy. Whether it be from a natural source like the sun or from a man-made source like a bulb, all forms of light make our life easier and better. Do you know this interesting fact about light that it can only travel in a straight path? This property is also known as rectilinear propagation. There are various other exciting concepts covered in the class 10 light chapter. Read on to learn more about it!

Introduction to Class 10 Light – Reflection And Refraction

Class 10 light chapter describes light as an essential element which makes things visible to us. Light originates from a point source and then bounces back as perceived by the eyes. Technically, light is the representation of a form of energy that results from the sensation of sight. Hence, light reflection occurs when the beam of light bounces back to the same surface after striking the surface of any object. Light refraction occurs when the medium of light gets changed from one form to another form.

Understanding Reflection of Light

The mechanism of when the light bounces back from the surface of its origin to the same medium is known as a reflection of light. The key terms in this segment are:

• Incident Light– Incident light or incident ray falls on the surface of the object
• Lightray- it is the line that forms the uni or bi-directional wave
• Light beam- it is the bunch of light rays
• Parallel beam- it has the parallel light rays 
• Reflected Light– Reflected light or reflected ray goes back to the medium after reflection
• The Angle of Incidence– It is the angle formed between the reflected ray and normal (normal is the plane)
• Principal axis– it is the line joining the centre of curvature and pole of a spherical mirror
• Pole- it is the geometrical Central point of are reflecting spherical surface which is denoted by P
• Aperture- Aperture is the width of the reflecting spherical surface
• Centre of curvature- the centre of curvature is the centre of a hollow spherical mirror
• The radius of curvature- the distance between the centre of curvature and the pole is known as the radius of curvature. The radius of curvature of the hollow sphere refers to the part of the mirror.
• Focus Point- the point on the principal axis where parallel light rays meet after the reflection is known as the principal focus or focal point. It is denoted by F
• Focal length– the distance between the focus point and pole is known as the focal length

Laws of Reflection of Light

There are two laws of reflection. Class 10 light chapter explains both of them in detail. Let’s understand them further in detail:

1. The angle of incidence is always equal to the angle of reflection.
2. The incident ray, the reflected ray, and the normal/perpendicular at the point of incidence lie in the same plane. 

Types of Mirror

The mirror is a  surface that reflects light. Another important aspect covered in the class 10 light chapter is the type of mirrors. Students must learn how to draw the ray diagrams in contrast with the mirror and the type of ray. There are 2 kinds of mirrors:

• Plane Mirror– A reflecting surface that is a plane.  
• Spherical Mirror– A  reflecting surface that is part of a hollow sphere. 

Characteristics of Images Formed by Plane Mirror

Any image formed by reflection from a plane mirror will have the following characteristics- 

1. Virtual and Erect- It refers to the image that cannot be formed on the screen whereas real images are recorded on the screen.
2. It is laterally inverted, that is, the left side of the object appears on the right side of the image.
3. The size of the image is always equal to the size of the object.
4. The image formed on the screen is far behind the mirror and the object is located on the front of it.

Spherical Mirror

Imagine a big hollow ball of mirror that is completely polished from the inside and the outer layer is coated with mercury so that no light comes out it. If we cut out a piece from that spherical ball, then, it will be known as a spherical mirror. Mentioned below are the vital terminologies related to spherical mirror derived from the class 10 light chapter-

• Principal Axis– It is the line joining the centre of curvature and pole of a spherical mirror
• Pole– It is the geometrically central point of a reflecting spherical surface which is denoted by P.
• Aperture– Aperture is the width of the reflecting spherical surface.
• Centre of Curvature– The centre of curvature is the centre of a hollow spherical mirror.
• Radius of Curvature– The distance between the centre of curvature and the pole is known as the radius of curvature. 
• Focus Point- The point on the principal axis where parallel light rays meet after the reflection is known as the principal focus or focal point. It is denoted by F.
• Focal Length- The distance between the focus point and pole is known as the focal length.

Types of Spherical Mirror

As per the side polished side of the spherical mirror, is dived into two types, they are-

• Convex Mirror- In a convex mirror, the reflecting surface is convex. This surface diverges the light ray, so it is also known as a diverging mirror.
• Concave Mirror- In a concave mirror, the reflecting surface is concave. This surface converges the light ray, so it is also known as a converging mirror.

Image Formation in Convex and Concave Mirror

If we go on and change the position of the object, you will notice that the characteristics of the image formed tend to change even after the slightest change in the position of the object. Mentioned below are some common laws of image formation from the class 10 Light chapter through which we can understand the properties of an image-

1. A Ray of light which is parallel to the principal axis always passes through the focus. 

2. A light ray that passes through the centre of curvature will retrace the source point after reflection.

3. A light ray on the pole gets reflected at the same angle on the other end of the principal axis.

Note- The light ray which passes through the centre of curvature of a reflecting spherical surface acts as a normal at the point of incidence. If the normal is known then an angle of incidence and reflection can be drawn easily. Also, the image will only be formed when the light rays meet at a point.

Spherical Mirror Sign Convention

For understanding the chapter in-depth, it is necessary to be familiar with the sign convention that is used while solving numerical problems related to mirrors.

• The object is placed on the left side of the mirror
• All the measurements are taken from the pole, parallel to the principal axis
• P is taken as and origin 
• The right side of the origin of the mirror is taken as positive
• The left side of the origin of the mirror is taken as negative
• The perpendicular that lies above the principal axis is taken as positive
• The perpendicular that lies below the principal axis is taken as negative
• f is the distance between Focus and the pole
• v is the distance of the image from the pole
• u is the distance of the object from the pole
• R is the distance between the pole and centre of curvature

Uses of a Concave Mirror

The concave mirror is used for various purposes-

• It is used in searchlights, and torches on the headlight of vehicles.
• It is used to see the image in a shaving mirror.
• It is used by dentists to see images of teeth.
• Very large concave mirrors are used to focus the sunlight in solar furnaces. 

Also Read: Concave Mirror and Lens

Uses of a Convex Mirror

A convex mirror is used in vehicles for rear view because it gives an erect image of the object. It also helps the drivers to view large areas for better understanding.

Also Read: Convex Mirror and Lens

Understanding Refraction of Light 

To prepare for board exams, you must thoroughly understand the class 10 Light chapter as it entails some important concepts related to upcoming chapters. A comprehensive study of reflection and refraction of light will assist students in solving problems with accuracy. 

Whenever a ray of light gets bent at an interface of different mediums, then it is known as the refraction of light. 

The change in the direction of propagation of light is not random, rather it depends upon the change of medium that is occurring. The optical density of the medium determines the direction in which the ray of light will bend. Let us understand the change in various media- 

1. Optical Rare- It is when the velocity of light rays in the medium is more. For example, the air is optically rare. 
2. Optical Dense- It is when the velocity of the light in the medium is less. For example, glass is denser than air. 

Must Read: Refraction of Light

Refractive Index

One of the essential topics of this chapter is the Refractive Index. The Refractive Index represents the extent or the total amount of bending of light when it passes from one medium to another. The types of refractive index are:

Relative Refractive Index– The refractive index of the medium with respect to the other medium is known as a relative refractive index. 

The refractive index of one medium with respect to another medium = speed of light in medium 2 (V2)/speed of light in medium 1 (V1)

Absolute Refractive Index- The refractive index of one medium with respect to vacuum or air is known as an absolute refractive index.

The absolute refractive index of the medium (m)
=  Speed of light in the air (c)/ Speed of light in a medium (Vm)

Terms Related to Refraction of Light

To get a better hold of this topic from the class 10 Light chapter, you must get familiar with these terms-

• Incident Ray– The incident light or the incident ray is the incoming ray on the refracting surface.
• Refracted Ray– The refracted light or the reflected ray is the outgoing ray from the reflecting surface.
• Angle of Incidence (i)- The angle of incidence is the angle formed between the incident rays and the normal/perpendicular line at the point of their incidence.
• Angle of Refraction (R)– The angle of refraction is the angle formed between the refracted rays and the normal/perpendicular line at the point of their incidence.
• Lens- It is the transparent refracting medium which is bounded by the two surfaces where at least one of them is curved. The refracting lens is of two types, that is, Concave and Convex lenses. 

Laws of Refraction of Light

According to the laws of refraction, major postulates are given as-

1. The incident ray, the refracted ray, and the normal/perpendicular at the point of their incidence lie in the same plane.
2. The ratio of the sine of the angle of incidence to the sine angle of refraction is always constant. 

The common phenomena that take place in day-to-day scenarios due to refraction are 

• Rainbow
• Light bending in a glass of water
• Camera lenses
• Object this location to water
• Binocular 

To understand Total Internal Reflection, read our detailed blog!

Sign Convention by a Spherical Lens

Just like a spherical mirror, in the sign convention for spherical lenses, the distance is measured from the centre.  The only difference is that measurements are taken from the optical centre, i.e., O instead of the centre of curvature. 

O- Optical Center
f- It is the distance between O and F
u- It is the distance of the object from O
v- It is the distance of the image from O
R- It is the distance between centre of curvature and O

The magnification of the object is defined as the ratio of the height of the object to the height of the image. It is related to u and v.

Power of Lens

The degree of convergence or divergence of the light ray which is achieved by a lens is known as the power of the lens. The power of the lens is also defined as the reciprocal of focal length and it is represented by the letter P. The SI unit is diopter and it is denoted by D. The power of the concave lens for a diverging lens is always taken as negative.

Virtual Image and Real Image

While attempting the numerical of the class 10 Light chapter, you will find that there are various questions that require one to have a prior understanding of the nature of the image. An image is a point where at least two or more light rays meet or appear to be meeting. Real images are formed when the light rays meet. Virtual images are created when the light rays appear to meet. Real images can be obtained on screen, and virtual images cannot be obtained on the screen. Real images are inverted, and virtual images are erect.

FAQs

Thus, we hope that through this blog on Class 10 Light: Reflection and Refraction, we have helped you in understanding an important chapter of class 10. The crucial decision of stream selection must be made after seeking expert guidance. Our experts at Leverage Edu are here to help you in making the best career choices.