As already stated, light is a form of energy that causes a sensation of vision in the eyes and allows us to see things. The study of light in physics is known as Optics, and it is an essential concept for advanced physics. Light causes a sensation of vision in the eyes. For example, light from a torch and motorcycles causes a sensation of sight in the eyes. Light always travels in a straight line unless the direction of light is changed using reflection and refraction concepts.

Reflection is a phenomenon when the light bounces back to the emitting medium after striking a surface. Different surfaces react differently when the light strikes:

• Opaque surface: In the case of opaque surfaces, the whole light beam gets reflected. So, opaque surfaces help in the reflection process. 
• Translucent surface: In fine characters, a portion of the light beam is reflected while the rest is transmitted through the surface. So, translucent surfaces partially help in the reflection process. 
• Transparent surface: In the case of transparent surfaces, the whole light beam gets transmitted through the surface, and reflection does not take place. So, transparent surfaces do not help in the reflection process of light.

• This law states that when a light beam is reflected upon a smooth opaque surface, the angle formed by the reflected ray is equal to the angle formed by the incident ray with respect to the perpendicular formed from the point of contact on the surface. 
• It also states that the incidence ray, the perpendicular, and the reflected ray lie in the surface’s same plane.
  
  Formula: Angle of reflection = Angle of incidence

Following are the properties of images formed by the mirrors:

• The image formed is virtually erect.
• The size of the source and the image formed is precisely the same.
• The distance between the images formed and the mirror is the same as the distance between the source and the mirror.
• The image formed in the mirror is inverted.

There are two broad types of mirrors:

• Plane mirrors  
• Spherical mirrors 
  • Concave mirror 
  • Convex mirror

Spherical mirrors are of 2 types:

• Convex mirror 
• Concave mirror 

Concave Mirror and Uses
Spherical mirrors with a reflected surface curved inwards are known as concave mirrors. They are also referred to as converging mirrors.
Uses of Concave Mirror:

• It is used as shaving mirrors in salons.
• Dentists use it to focus light on teeth by diagnosis. 
• They are used as headlights of cars to create a powerful source of light.
• It is used in satellite dishes to concentrate weaker signals together.

Convex Mirror and Uses
Spherical mirrors with a reflected surface curved outwards are known as concave mirrors. They are also referred to as diverging mirrors.
Uses of Convex Mirror:

• Convex mirrors are used as rear view mirrors in cars, which helps drivers look at the vehicles coming from behind.
• It is even used as security mirrors in ATMs, allowing the customer to see their image behind them.

The object’s image is formed in both the mirrors as the image in the first mirror becomes the object for the second mirror. The following are the characteristics of images included in a pair of mirrors:

• All the images are virtually erect.
• The size of the source object and the images formed are the same.
• The distance between the images formed and the mirror is the same as the distance between the source and the mirror. 
• The image formed in mirror 1 is inverted, while the image formed in mirror 2 is similar to the object.

According to the law of reflection, the angle of reflection is equal to the angle of incidence, which means that the distance between the mirrors and the object is the same as the distance between the mirrors and the image formed. Using this concept, the image’s location created in the plane mirror can be calculated as the distance is the same but in opposite directions.

A total of three images are formed when an object is placed between two perpendicular plane mirrors.

When an object is placed between a pair of parallel plane mirrors, an infinite number of images are formed.

Light is a straight line electromagnetic radiation of any wavelength visible to human eyes that can be deviated using reflection and refraction concepts. The chapter ‘Light’ is not only an essential topic for class 9th physics, but it is also a necessary concept for advanced physics. This chapter’s thorough knowledge will smoothen your journey through the upcoming physics and science chapters.

1. What is the angle of reflection?
   The angle of reflection is the angle formed between the reflected ray and the perpendicular at the reflection point.
2. What is the angle of incidence?
   The angle of incidence is the angle formed between the incident ray and the perpendicular at the reflection point.
3. How many images are formed when an object is placed between a pair of parallel mirrors?
   When an object is placed between a pair of parallel plane mirrors, an infinite number of images are formed.
4. How many images are formed when an object is placed between mutually perpendicular mirrors?
   When an object is placed between a pair of parallel plane mirrors, an infinite number of images are formed.