Introduction :

In our daily life, we observe different phenomena of light. But we can neither see nor touch the light. Actually, light is a very peculiar substance. Many scientists had researched the nature and properties of light. Finally, it is known that light has a dual nature that is particle nature as well as wave nature.

In this chapter, we will discuss the reflection of light.

Reflection of Light :

The word ” refelection “ means ” throw back from a surface “.

In the above picture, we can see the image of the leaf in water. Actually, this is due to reflection of light.

The above picture explains the image formed by the mirror which is nothing but the reflection of light.

Now let’s understand the refelction of light.

When a ray of light strikes on a surface, it reflects back in its own medium. This is called as the reflection of light.

Incident Ray: The light rays that strike on the surface are called Incident rays. In the above picture, red line shows the incident ray.

Reflected Ray: The rays of light that reflect back in its own medium are called Reflected rays ( blue line in the above figre ).

Point of Incidence: The poin on the surface at which the light rays strike on the surface, is called the point of incidence.

Normal: The perpendicular at the point of incidence is called the normal.

The angle of Incidence: The angle made by the incident ray and normal is called the angle of incidence.

The angle of Incidence: The angle made by the reflected ray and normal is called the angle of reflection.

Types of Reflection of Light :

There are two types of reflection of light

1 ) Regular reflection of light

2) Irregular reflection of light

1 ) Regular Reflection of Light

If the incident surface is smooth, then the reflection should be regular and this reflection is called as the Regular Reflection of Light. In this type of reflection, if the incident rays are parallel then the reflected rays also parallel. In this type of reflection, the image would be very sharp and clear.

2 ) Irregular Reflection of Light or Diffused Reflection of Light :

If the incident surface is not smooth that is rough surface, then the reflection of light would not be regular. This type of reflection of light is called as the irregular reflection of light. As the image formed due to this type of reflection is dull, this is also known as the Diffused Reflection of light.

Laws of Reflection of Light :

1 ) The incident ray, point of incidence, normal and the reflected ray are coplanar.

2 ) Angle of incidence is equal to the angle of reflection.

In the above figure, pink corner represents angle of incidence while purple corner represents angle of reflection and both are equal in magnitude.

Questions – Answer Discussion

1 ) Define reflection of light.

Ans :When a ray of light strikes on a surface, it reflects back in its own medium. This is called as the reflection of light.

2 ) Why reflection of light occurs ?

Ans : The light rays always travel in a straight line in a particular medium and it is the rectilinear propagation of light. Whenever a light rays falls on a transparent, translucent or opaque surface or any surface that does not abosrbs energy of the radiation, it bounces away from the surface. In this way, the refleciton of light occurs.

3 ) Define the following terms:

( a ) incident ray ( b) reflected ray ( c) angle of incidence ( d ) angle of reflection

Ans : ( a ) Incident ray : The light rays that strikes on a surface is called as the incident ray. In the following figure, red line denotes the incident ray.

( b ) Reflected ray : The light rays that bounce away from the incident surface, is called as the reflected rays. In the above figure, the blue line indicates the reflected rays.

( c ) Angle of incidence : The angle made by the incident light ray with the normal is called as the angle of incidence.

( d ) Angle of reflection : The angle made by the reflected ray with the normal, is called as the anngle of reflection.

4 ) What are the different types of reflection of light ?

Ans : There are two different types of refleciton of light. One is Regular reflection of light and other is irregular refelction or diffused reflection.

5 ) What are the difference between regular and irregular refelction of light ?

Ans :

Regular Reflection of Light Irregular Reflection of Light
1 ) It requires smooth surface.1 ) When the surface is rough, the reflection would be diffused or irregular.
2 ) In this case, all reflected rays are parallel.2 ) In this case, all the reflected rays are not parallel.
3 ) In this type of reflection, the light rays reflected in a paricular direction.3 ) In this type of reflection, the light rays are not reflected in a particular direction.
4 ) A very sharp image is formed.4 ) Dull image is formed.
5 ) Examples : Image formation by mirror and new and unused spoon etc.5 ) Examples : Image formation by plastic and paper etc.

6 ) What are the laws of reflection of light ?

Ans : ( 1 ) The incident ray, reflected ray and normal at the point of incidence are coplanar.

( 2 ) Angle of incidence is equal to the angle of reflection.

7 ) Give a natural phenomenon in which reflection of light occurs.

Ans : Rainbow is an optical phenomenon that occurs due to the reflection of light as well as refraction of light.

8 ) What is the nature of light ?

Ans : Light has dual natrue that is particle nature as well as wave nature.

9 ) If angle of incidence is 35 degree then what will be the value of angle of reflection ?

Ans : 35 degree.

10 ) If angle made by the incident ray with the incident surface is 25 degree, then what will be the angle of reflection ?

Ans : Required angle of incidence = 90 – 25 = 65 degree

11 ) A ray of light incidents on a smooth surface, it reflects back making an angle of 75 degree with the surface, then what was the angle of incidence ?

Ans : Required angle of incidence = 90 – 75 = 15 degree

12 ) A ray of light incidents on a rough surface making an angle of 15 degree with the normal to the surface. What will be the angle made by the reflected ray with the surface.

Ans : Required angle = 90 – 15 = 75 degree

13 ) Does shadow form due to reflection of light ? Explain your answer.

Ans : No, Shadow is not formed due to the refelction of light. It is formed due to one of hte unique property of light that is rectlinear propagation of light.

14 ) What is rectilinear propagation of light ?

Ans : Light rays travel in a straight line. This property of light is called as Rectilinear Propagation of light.

15 ) Guess…………. you are looking your face in a spoon. You saw your face. How this is possible ?

Ans : The surface of a spoon is one of the smooth surface. It produces a sharp image by the refelction of light. At the concave part, one can see the inverted image while at the convex part of the spoon, the image is erect. This is possible due to the concave and convex structure of the spoon.

16 ) In the above question, what is the nature of your image ? Is the image inverted ?

Ans : At the concave part of the spoon, the nature of the image is real and inverted. At the convex part of the spoon, the nature of the image is virtual and erect.

17 ) What is the relation between angle of incidence and angle of reflection ?

Ans : They are equal in magnitude.

18 ) What is the relation between rectilinear propagation of light and reflection of light ?

Ans : As we know that the light rays always travel in a straight line, that’s why whenever any surface comes in its path, it bounces or reflect back in its own medium.

19 ) What type of surface is needed to reflect the incident ligt rays so that the image produced is sharp ?

Ans : Smooth surface.

20 ) If the light rays fall on water surface, what will happen ?

Ans : If the light rays fall on water surface, its some parts are reflected, some are refracted and rest parts are absorbed by the surface.

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