How Does Light Interact With Matters? Reflection, Absorption, Transmission

We will learn in this session how does light interact with matters. We will illustrate a couple of examples for better understanding. Let’s explore.

How Does Light Interact With Matters?

Like other substances, Light also interacts with matters. To understand, we will take one mirror, one football, and one glass.  Now, if we bring all the objects under light, we will see, each object will interact with light differently. If we take another few objects also, there will be three scenarios:

  • Light can be bounced back from the object 
  • Light can be absorbed 
  • Light can pass through the object
how does light interact with matters reflection absorption transmission
Fig. 1 Reflection absorption transmission

Look at the diagram, 

  • When light bounces back from the object is known as Reflection.
  • When light absorbed by the object is known as Absorption.
  • When light passes through the object is known as Transmission.

What is Reflection of Light?

Reflection means bouncing off the light from an object. We have seen reflection happened in the mirror because the surface of the mirror is very smooth and shiny. The smooth and shiny surface can be:

  • Mirror
  • Water surface
  • Polished metal surface etc.
reflection light
Fig. 2 Reflection of light

There are a few rules of reflection, which we will study later. 

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What Is Absorption of Light?

Absorption of light means if the light falls on an object, the object will absorb the light. We have seen absorption in football. Absorption of the light can happen on so many objects: 

  • Football
  • Book
  • Brick etc.
absorption light
Fig. 3 Absorption of light

What Is Transmission of Light?

Transmission means when light passes through the object. We have seen transmission in the glasses. The object can be:

  • Glass
  • Water
  • Air etc.
transmission light
Fig. 4 Transmission of light

Difference Between Reflection, Absorption & Transmission

There are a few differences between Reflection Absorption & Transmission. These are: 

Reflection Absorption Transmission
When Light rays fall on an object, it will bounce off When Light rays fall on an object, it will be absorbed  When Light rays fall on an object, it will be passed through the object 
Reflection happens on a shiny surface Absorption happens on any surface other than very shiny surfaces Transmission happens on transparent type surfaces 
Example: Mirrors, Plain water surface, etc. Example: Brick, book, etc. Example: Glass, water, air, etc.
reflection from object
Reflection from object
absorption in object
Absorption in object
transmission through object
Transmission through object

What Happens in the Mirror – Reflection, Absorption, or Transmission?

The mirror is made of glass, hence, it is very simple to conclude that transmission will happen. Why do we use a mirror? To see ourselves, basically, we see our images and comb our hair! However, if transmission happens in the mirror then we should not have seen our images.

what happens in mirrors
Fig. 5 What happens in the mirrors?

Then how is it possible? If we observe carefully, we will see that there is a coating of silver nitrate in the back of the mirror and due to that coating, light rays can not pass through the glass of the mirror & bounces back to our eyes and we see ourselves. 

mirror coating
Fig. 6 Mirror coating

Hence, though it is glass, due to coating, light rays will be reflected. There may be very little absorption but since the surface is very shiny, absorption is negligible. 

reflection happens in mirror
Fig. 7 Reflection happens in the mirror

Further Study

Reference

  • NCERT Books
  • Our Own Experience

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