# Class 10 Chapter 10 Light- Reflection of Light Notes

## Reflection of Light Notes

Contents

In this article, we are providing you with the best short and concise Reflection of Light notes. These Reflection of Light notes will surely help you fetch good marks in your CBSE board exams.

Class 10 Chapter 10 consists of two topics- Reflection of Light and Refraction of Light, but in this post, we are only providing you the reflection of light notes.

Reflection of Light Notes Overview

The list of topics that we will discuss in this article are-

• What is Light
• Nature of Light
• Reflection
• Laws of Reflection
• Kinds of Reflection
• Reflection by Plane Mirror
• Spherical Mirrors
• Important Terminology
• Reflection by Spherical Mirrors
• Reflection by Concave Mirror
• Uses of Concave Mirror
• Reflection by Convex Mirror
• Uses of Convex Mirror
• Sign Convention
• Mirror Formula
• Magnification
• Numericals

### What is Light?

Define Light.

Light can be defined as follows-

It is an electromagnetic transversal wave that enables us to see objects around us by producing the sensation of sight in our eyes.

In a simpler way, it can be defined as a form of energy that produces the sensation of sight.

Some Key Characteristics of Light

Light travels in a straight light.

Light is an electromagnetic wave. It doesn’t need any medium to travel.

It travels with a speed of 3 × 10^8 m/s or 3 × 10^5 km/s in vacuum.

The speed in other media is different for light. It travels at a speed of 225000 km/s.

Light undergoes reflection when falls on a polished surface, and refraction when travels from one medium (transparent) to another.

### Nature of Light

Light behaves as a particle and waves both.

In the 17th century, Isaac Newton considered light to be a stream of particles.

His theories were based on the observations of phenomena like reflection and refraction.

But scientists like Christian Huygens, and his rival Robert Hooke thought of light as a wave.

Wave theory was not accepted immediately but experiments like the ‘double slit experiment’ by Thomas Young found that light behaves like a wave, not a particle.

Maxwell in 1873 proposed that light was a form of high-frequency electromagnetic wave and Hertz confirmed it experimentally in 1887.

Again in the 20th century, it became evident that wave theory is not sufficient to explain the nature of light.

The photoelectric effect again shows that light has a particulate nature.

Modern theory suggests that light is neither a wave nor a particle, it has a dual nature, i.e., sometimes behaves like a particle and sometimes like a wave.

### Reflection

What is Reflection?

Reflection is the phenomenon in which the ray of light after falling on a smooth polished surface bounces back in the same medium.

Incident Rays: The incoming light rays from the source that fall on a surface.

Reflected Rays: The outgoing light rays after reflection from the reflecting surface.

Normal: It is the line perpendicular to the reflecting surface at the point of incidence.

Angle of Incidence or Incident Angle (∠i): It is the angle between the incident ray and the normal.

Angle of Reflection (∠r): It is the angle made by the reflected ray with the normal.

#### Laws of Reflection

What are the different laws of reflection?

There are two laws of Reflection

Law 1: The angle of incidence is always equal to the angle of reflection or vice versa.

∠i = ∠r

Law 2: The incident ray, the reflected ray, and the normal at the point of incidence, all lie in the same plane.

Note: Laws are applicable to all kinds of mirrors.

#### Types of Reflection

There are mainly two types of reflection if we consider the nature of the reflecting surface-

1. Regular Reflection or Specular Reflection

2. Irregular Reflection or Diffused Reflection

What is Regular Reflection of light?

or

What is the Specular Reflection of Light?

In regular reflection or specular reflection of light, the incident parallel beams of light after reflection are parallel to each other.

What is Irregular Reflection or Diffused Reflection?

In this type of reflection, the parallel incident rays after reflection are reflected randomly in various directions.

### Reflection by Plane Mirror

The topic of reflection by the plane mirror was already discussed in your class 8 light chapter.

#### Characteristics of Image Formed by Plane Mirror

• The image is virtual and erect
• Image size, i.e. the height, is equal to object size (hi = ho)
• Magnification = 1
• The image is laterally inverted
• The image distance from the mirror is equal to the object distance from the mirror (u = -v)

### Mirrors

What are mirrors?

Mirrors are the highly polished reflecting surface.

What are the types of mirrors?

There are mainly two types of mirrors-

1. Plain Mirror– The reflecting surface is a plane.

2. Spherical Mirror or Curved Mirrors

The types of mirrors whose polished smooth reflecting surface is either curved inward or outward.

The name of these mirrors is spherical because the polished reflecting surface is part of a hollow sphere of glass.

#### Types of Spherical Mirrors

There are mainly two types of spherical mirrors depending on the nature of the reflecting surface-

1. Concave Mirror– reflecting surface is curved inward

2. Convex Mirror– the reflecting surface is curved outward.

### Spherical Mirrors

#### Important Terminology of Spherical Mirrors

Let us now talk about some of the important terms related to spherical mirrors. These Important terminologies of Spherical Mirrors will help you in describing the image formation.

##### Centre of Curvature (C)

What do you understand by the center of curvature of a spherical mirror?

The Centre of Curvature is the center of the circle or the hollow sphere of which the spherical mirror is a part. It is denoted by the letter C.

##### Pole (P)

The pole of the mirror is the central point of the mirror. It is denoted by the letter P. The Pole of the mirror is taken as the reference point for the measurement of distances from the mirror.

##### Aperture

It is the effective width of the mirror from which the reflection of light takes place.

It is denoted by the letter R. It is the radius of the circle or the hollow sphere of which the mirror is a part. It can also be defined as the distance between the Centre of Curvature and the Pole.

##### Focus (F)

Focus is denoted by the letter F. It is also called the focal point.

When rays parallel to the principal axis from infinity either meet or appear to meet after reflection at a point on the principal axis, the point is called Focus.

##### Focal Plane

It is an imaginary plane perpendicular to the Principal Axis and passing through focus.

##### Focal Length (f)

It is denoted by the letter f. It is the distance between the focus and the pole.

##### Principal Axis

Define the Principal Axis.

The Principal Axis is the imaginary line passing through the center of curvature and the pole of the mirror.

##### Normal

line joining the center of curvature and any point on the spherical mirror.

##### Object distance (u)

It is the distance between the pole and the position of the object.

##### Image distance (v)

It is the distance between the pole and the position of the image so formed.

##### Virtual Image vs Real Image

What is the difference between the virtual image and the real image?

A virtual image is erect whereas the real image is inverted.

A virtual image of an object can’t be obtained on a screen whereas a real image can be obtained on a screen.

In a virtual image, the reflected rays appear to meet whereas in the real image, the reflected rays actually meet or intersect.

### Reflection by Concave Mirror

The reflection of light from the concave mirror follows the same laws as it was in the case of plain mirrors.

#### Image Formation by Concave Mirror

For image formation by a concave mirror, consider any two of the following rays of light-

1. Rays of light parallel to the principal axis pass through the focus after reflection
2. Rays of light passing through the focus will reflect parallel to the principal axis.
3. Ray of light passing through the centre of curvature will reflect back in the same path
4. Ray of light falling at the pole will reflect as per the law of reflection (∠i = ∠r)

Types of Image Formed at different Object positions

##### 1. When the Object is kept at Infinity

When light from an object at infinity falls on the concave mirror-

• Image Position- at focus
• Nature- Real & Inverted
• Size- very diminished
##### 2. When the Object is kept beyond C
• Image Position- between Centre of Curvature (C) and Focus (F)
• Nature- Real & Inverted
• Size- diminished
##### 3. When the Object is kept at C
• Image Position- at the Centre of Curvature (below)
• Nature- Real & Inverted
• Size- same (equal)
##### 4. When the Object is kept between C and F
• Image Position- beyond Centre of Curvature (C)
• Nature- Real & Inverted
• Size- Enlarge
##### 5. When the Object is kept at Focus (F)
• Image Position- at infinity
• Nature- Real & Inverted
• Size- very large
##### 6. When the Object is kept between Focus and Pole (P)
• Image Position- behind the mirror
• Nature- Virtual & Erect
• Size- Enlarged

#### Uses of Concave Mirror

What are the uses of concave mirrors?

There are many uses for concave mirrors. Let us summarize some of the uses of concave mirrors.

• Used by dentists
• Used as a shaving mirror
• Used in torches, floodlights, etc
• Used in Solar cookers for heating

### Reflection by Convex Mirror

The reflection of light from the convex mirror follows the same laws as it was in the case of plain mirrors.

#### Image Formation by Convex Mirror

For image formation by a convex mirror, consider the following rays of light-

1. Rays of light parallel to the principal axis appear to come from the focus from behind the mirror
2. Ray of light passing through the Centre of Curvature will reflect back in the same path

Types of Image Formed at different Object positions

##### 1. When the Object is kept at Infinity

When light from an object at infinity falls on the concave mirror-

• Image Position- behind the mirror at the focus
• Nature- Virtual and Erect
• Size- very diminished
##### 2. When the Object is kept between infinity and Focus
• Image Position- behind the mirror between pole (P) and Focus (F)
• Nature- Virtual & erect
• Size- diminished
##### 3. When the Object is kept in Focus
• Image Position- behind the mirror halfway (f/2) between pole (P) and Focus (F)
• Nature- Virtual & erect
• Size- Smaller
##### 4. When the Object is kept between Focus and Pole (P)
• Image Position- behind the mirror between pole (P) and Focus (F)
• Nature- Virtual & erect
• Size- Smaller

#### Uses of Convex Mirror

What are the uses of convex mirrors?

There are many uses for convex mirrors. Let us summarize some of the uses of convex mirrors.

• As rear-view mirror in vehicles
• As vigilance mirrors in stores, roads
• Used in buses over the stairs or in the front for safety

### Sign Convention

In order to solve light numerical class 10, we need to know some of the sign conventions.

• Pole of the mirror is considered the reference point or the origin
• Distances are measured from the pole
• The object is always kept at the left of the mirror, so incident light comes from the left of the mirror and the direction of the incident light is taken positive.
• Distance to the left of the pole is taken negative (opposite to the direction of)
• Distances to the right of the pole are taken positive
• Distances above the Principal axis are taken positive
• Distance below the Principal axis is taken negative

### Mirror Formula

The mirror formula is the mathematical relationship between the object distance (u), image distance (v), and the focal length (f) of the mirror.

1/f = 1/v + 1/u

### Magnification

It is the relative extent to which the image of an object is magnified.

It can also be defined as the ratio of the height of the image to the height of the object.

M = hi/ho

Magnification can also be defined as

M = – image distance/object distance

M = -v/u

• When M = 1 then image height = object height
• When M>1 then the image is magnified or the image height is greater than the object height
• When M<1 then the image is diminished or the image height is smaller than the object height

We hope you like this Reflection of Light Notes.

### Basic Numericals

Q1. What is the focal length of a convex mirror whose Radius of Curvature is at a distance of 30 cm from the pole of the mirror?

We know, R = focal length (f)÷2 = 30 cm ÷ 2 = 15 cm [Ans]

2. A concave mirror produces four times magnified real image of an object placed 12 cm in front of it. Where is the image located?

Answer: Note: Take care of sign conventions

Given: u = – 12 cm, M = – 4

To find: v=?

We know, M = – v/u ⇒ -4 = -v/-12 ⇒ v = -48 cm

Therefore, the image will be formed at a distance of 48 cm in front of the mirror.

Hope, you liked these few sample basic numerical. We will soon upload more numerical separately.

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