Reflection of Light 

Key Concepts

• Reflection of light
• Terms related to the reflection of light
• Laws of reflection
• Types of reflection
• How do we see objects?

Introduction: Reflection of Light 

It is known that the opaque objects reflect some light falling on them and absorb the rest. However, they do not transmit light through them. Some opaque objects reflect a considerable amount of light from their surface that they can form an image of an object located in front of them on their surface. Such objects include the well-polished and smooth surfaces of a mirror, a table top and a stainless-steel plate and spoons. In this section we shall revisit the concepts of reflection, laws and types. 

Explanation: 

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. The smoother and more polished the surface of an object is, the more light it reflects. The more light an object reflects, the clearer the image of another object appears on its surface. Mirror and objects with polished and smooth surfaces like a tabletop, steel plate and spoons reflect most of the light that falls on their surface. The reflection of an object on a mirror is called an image of that object. 

Terms related to reflection of light: 

There are some terms that are used universally to discuss the reflection of light when it falls on a surface. They are as follows: 

1. The surface that reflects light is called a reflecting surface. 

2. A ray of light that hits the reflecting surface is called an incident ray. 

3. The incident ray after reflecting off the surface is called the reflected ray. 

4. The point at which the incident hits the reflecting surface is called the point of incidence. 

5. An imaginary line is always drawn perpendicular to the reflecting surface at the point of incidence, called the normal. 

6. The angle made by the incident ray with the normal is called the angle of incidence (i). 

7. The angle made by the reflected ray with the normal is called the angle of reflection (r). 

Laws of reflection: 

Light follows two laws whenever it gets reflected off any surface. They are as follows: 

1. The incident ray, the reflected ray and the normal at the point of incidence, all lie on the same plane. 

2. The angle of incidence is equal to the angle of reflection.  

                                     i = r 

An incident ray hitting the reflecting surface is said to be incident normally on the surface if it goes along the normal. The reflected ray follows the same path as that of the incident ray but in opposite direction. In such a case the angle of incidence = angle of reflection = 0 degrees. Similarly, when the angle of incidence is 90 degrees, the angle of reflection is also equal to 90 degrees. In such a case, the light ray goes along the reflecting surface as shown below. 

Types of reflection: 

Reflection of light occurs in two ways depending upon the nature of the surface by which it is getting reflected. They are as follows: 

Regular reflection: 

• When a surface is highly smooth like in case of a mirror, then the image formed after reflection is sharp and clear. 
• This type of reflection of light that takes place when it reflects off a highly smooth surface is called regular reflection. 
• When a beam of light incidents on the surface of a mirror, the reflected rays are also parallel to each other. This is the reason behind sharp and clear images. 

Diffused (Irregular) reflection: 

When a surface is even slightly rough like in case of a wooden table, then the image is either not formed or is blurred if it forms. 

This type of reflection of light that takes place when it reflects off a rough surface is called diffused or irregular reflection. 

When a beam of light incidents on the surface of a mirror, the reflected rays are not parallel to each other but randomly directed. This is the reason behind blurred or no images. 

How do we see objects? 

• When light from a luminous object falls on an object, it reflects off its surface in all directions, as a result of diffused reflection.  Some of this reflected light enters our eyes. 

• The eye lens focuses the light entering our eyes on to a layer, which lies at the back of the eye, called the retina. Here, a real and inverted image of the object is formed. 
• The signals from the retina are transmitted to our brain, which interprets them and shows us an upright image of the object. 

Summary:

• When light falls on an object, it gets reflected, transmitted or absorbed.
• Reflection is a phenomenon of light bouncing off the surface of an object.
• The smoother and more polished the surface of an object is, the more light it reflects.
• The more light an object reflects, the clearer the image of another object appears on its surface.
• 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.
• The incident ray, the reflected ray and the normal at the point of incidence, all lie on the same plane.
• The angle of incidence is equal to the angle of reflection. i=r
• The type of reflection of light that takes place when it reflects off a highly smooth surface is called regular reflection.
• The type of reflection of light that takes place when it reflects off a rough surface is called diffused or irregular reflection.
• When light from a luminous object falls on an object, it reflects off its surface in all directions. We see the object when some of this reflected light enters our eyes.