6th Class Science Light, Shadows and Reflections Reflection of Light

     Reflection of Light

Reflection of light occurs, when a beam of light, falls on a reflecting surface. Let's study about them in detail.

          Reflection of light by a Plane Mirror

A glass with painted one side is called a plane mirror. A most important application of a plane mirror is the formation of image. Incident light on the plane mirror is reflected at the same angle at which the ray of light is incident on the mirror. The backside of a plane mirror does not allow the beam of light to pass through it, hence the beam of light is reflected by the surface of the mirror,

Look at the following picture of reflection of light by a plane mirror:

In the picture above, incident ray from a torch fall on the surface of the plane mirror with an angle of \[{{\theta }_{1}}\] and reflected by the plane mirror with an angle of \[{{\theta }_{R}}\]. According to the laws of reflection by a plane mirror:

(i) The angle of incident with respect to the normal is equal to the angle of reflection.

(ii) The incident ray, reflected ray and normal lie on the same plane.

(iii) The incident ray and the reflected ray are on the opposite sides of the normal.

         Reflection of Light by a Rough Surface

If a beam of white light strikes on the rough surface, it defuses in different directions. The beam of white light diffuses in different directions due to the irregularity of the surface.

Look at the following picture of diffused reflection:

          Image Formed by a Plane Mirror

Every plane and shiny object forms image. Image is formed by the reflection of light. When light strikes an object, some amount of light is absorbed by the object itself and some are reflected back as shown in the figure given herewith. The incident beam of light from the object on the plane mirror is reflected and reflected beam of light is detected by the detector which is the result of formation of the image of that object. The distance between the plane mirror and object is same as the distance between the surface of the mirror and image formed. Therefore, the sum of the both distances in opposite directions is always zero. The image formed by a plane mirror cannot be obtained, hence the image which is formed by the plane mirror is called virtual image. When we place a thing in front of a plane mirror, left part of the thing appears at right and right part appears at left, therefore, the image formed by a plane mirror is called lateral inverted image and this characteristic of a plane mirror is called lateral inversion.

         Formation of Multi Images by Plane Mirrors

Single image is formed by a plane mirror, when an object is placed in front of it. Two or more images can be formed by the use of two mirrors. Do the following to observe the multi images formed by two plane mirrors

Set two mirrors at right angle to each other with their edges touching. Place an object between them. Three images will be formed by both the plane mirrors.

Look at the following picture to understand the formation of multi images by two plane mirrors:

Human Eyes

We see things due to the reflection of light from the things. Our eyes cannot see anything in the dark. The shape of our eyes is spherical. The white part of our eyes protect the inner part of the eyes from injury. The transparent front part of the eyes is called cornea. A dark structure behind the cornea is called iris. Pupil is the small opening in iris. The colour of eyes depends on the colour of iris. Lens of our eyes are located behind the pupil. The lens focuses light on retina. Retina sends the signal to the brain.

Look at the following picture of human eye:

       What happens when a beam of light is incident on a plane mirror at an angle of 30°?

(a) Angle of incident is equal to the angle of reflection

(b) Angle of incident is greater than the angle of reflection

(c) Angle of incident is smaller than the angle of reflection

(d) All of these

(e) None of these

Answer: (a)

Explanation 

On a plane mirror, angle of incident is equal to the angle of reflection. Therefore, option (A) is correct and rest of the options is incorrect..

         What will be the angle of reflection if more than one beam of light is falls on the rough surface?

(a) Beam of light will reflect at the same angle of reflection

(b) Beam of light will diffuse

(c) Beam of light will not reflect

(d) All of these

(e) None of these

Answer: (b)

Explanation

A rough surface diffuses incident beam of light. Therefore, option (B) is correct and rest of the options is incorrect..