Reflection of Light – Reflection, Transmission and Absorption

Reflection of light 

 Key Concepts

• Reflection, transmission and absorption
• Reflector of light
• Reflection of light
• How do we see objects?
• Smooth and rough surface

Introduction

It is known that opaque objects block most of the light that falls on them. This light which is prevented by an opaque object from getting through can undergo one or more processes among reflection, transmission, and absorption. 

Explanation

What happens when light falls on the surface of an object? 

Three things can happen to the light falling on any object. They are: 

1. Reflection 

2. Transmission 

3. Absorption  

Reflection: The process of bouncing off the surface of the object. 

Transmission: The process of getting through the object. 

Absorption: The process of getting absorbed by the object and converted to heat. 

The fraction of light that gets reflected, transmitted or absorbed by an object varies with the type of object chosen amongst transparent, translucent and opaque objects. 

Opaque objects reflect some amount of light and absorb the rest. They do not transmit light. 

Transparent objects transmit most light falling on them. They reflect a very small amount of light and absorb the rest. 

Translucent objects undergo all three processes, i.e., they reflect, absorb and transmit the light that falls on them. 

Reflector of light: 

In the picture below, the material on the left is a mirror, whereas the material on the right is a glass partition. We cannot see through the mirror at all. However, we can completely see through the glass partition. Thus, the mirror is opaque, whereas glass is transparent. 

We cannot see through a mirror at all. Thus, it is an opaque object. This is because no light passes through it. In other words, all the light that falls on the surface of a mirror bounces off, i.e., gets reflected. This is because of its highly smooth and polished surface. In fact, a mirror reflects 99.9% of light that falls on it. Hence, it is the best reflector of light. 

Reflection of light: 

The phenomenon of bouncing back of light when it falls on the surface of an object is called reflection of light. This is similar to the bouncing of a ball which is thrown on to a wall. 

A mirror is the best reflector of light. The reflection of light by a mirror is depicted by the figure below. When we see our face in a mirror, we are seeing the light from our face reflecting off the mirror. The reflection of our face on the mirror is called our image. 

The smoother and more polished the surface of an object, the more light it reflects. The more light an object reflects, the clearer the image of another object appears on its surface. For example, stainless steel plates and spoons can show the image of an object placed in front of them as they are able to reflect a considerable amount of light that falls on their surface. A well-polished surface of a table-top can also produce an image, as well-polished surfaces reflect more light as compared to the unpolished ones. 

The closer the football is moved to the light source, the bigger the shadow becomes. This is because the object blocks more and more light as it moves towards the source. The further the football is moved from the light source, the smaller the shadow becomes. This is because the object blocks lesser and lesser light as it moves away from the source. 

All the objects which can be seen by our eyes reflect some amount of light, if not all. For example, chair, table, walls , plants and animals etc. 

Thus, we can arrange the objects in descending order of the amount of light that reflects off its surface in the following manner. 

How do we see objects? 

When light from a luminous object falls on an object, some amount reflects off its surface in all directions. We see the object when this reflected light enters our eyes. 

Summary

1. When light falls on an object, it gets reflected, transmitted or absorbed.
2. Reflection is a phenomenon of light bouncing off the surface of an object.
3. Transmission is a phenomenon of light getting through an object.
4. The smoother and more polished the surface of an object is, the more light it
   reflects.
5. The more light an object reflects the clearer the image of another object appears on
   its surface.
6. Mirrors are the best reflectors of light. They reflect about 99.9% of light that falls on
   their surface.
7. Mirrors form an image of an object placed in front of them.
8. Polished surfaces like the surface of a stainless-steel plates and spoons and table
   tops also reflect a considerable amount of light so that they also form feeble images
   of objects placed in front of them.
9. When light from a luminous object falls on an object, it reflects off its surface in all
   directions. We see the object when this reflected light enters our eyes.