Reflection on a Plane Mirror: Laws, Uses, Image Formation

Reflection on a plane mirror is the process of obtaining a virtual and erect mirror image. This happens when light rays get stroked on the flat mirror and get reflected back. As per the laws of reflection, the angle of reflection is equal to the angle of incidence. An image is created behind the plane which is present on the mirror. 

Key Takeaways: Reflection, Reflection on a plane mirror, Laws of reflection, Image formation by plane mirror, Plane mirror, Light

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What is Reflection?

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When the light rays fall on any object, light is bounced back from the object and this process is known as the Reflection of light. The light reflected from the object falls into our eyes, making the object visible to us. All the things we see around us are because of reflection. 

The reflection of light depends on the type of object. A polished or smooth surface reflects most of the light falling on it, while a rough surface absorbs some amount of light and reflects back the rest of the light. The direction of reflected rays depends upon the surface of the object. 

Types of Reflection

The reflection of light can be classified into three types:

• Mirror Reflection
• Specular Reflection
• Diffuse Reflection

The light rays in Mirror reflection or Specular reflection, are reflected back in the same direction, whereas in Diffusion reflection the light rays are scattered in all directions. 

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Reflection on Plane Mirror

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A plane mirror is a mirror with a flat or planar mirror reflective surface. When the light rays fall on the plane mirror, the light rays bounce back from the surface of the plane mirror, known as Reflection of Light. Let us understand the reflection on Plane Mirror with a diagram.

• Incident Ray: The light rays falling on the surface of the plane mirror is called the incident ray of light.
• Point of Incidence: The point at which the light rays fall on the surface is called the point of incidence.
• Reflected Ray: The light ray bounced back from the surface of the plane mirror is called the Reflected ray.
• Normal: Normal is an imaginary line perpendicular to the surface of the mirror at the point of incidence. The normal equally divides the incident ray and reflected ray.
• Angle of Incidence: The angle between the incident ray and the normal at the point of incidence is called the angle of incidence. The angle of incidence is generally represented by θi.
• Angle of Reflected: The angle between the reflected ray and the normal at the point of incidence is called the angle of reflection. The angle of reflection is generally represented by θr.

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Laws of Reflection

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Laws of Reflection states that,

• The angle of incidence is always equal to the angle of reflection, i.e. θi = θr.
• The incident ray, reflected ray, and the normal at the point of incidence, all lie in the same plane.

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Image Formation by Plane Mirror

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The incident rays falling on the surface of the plane mirror are reflected back from the surface, forming an image. The image formed by the plane mirror is virtual and erect, which means the image is imaginary and upright (same as the object). 

Characteristics of Image formed by Plane Mirror

• The image is formed behind the plane mirror
• The image formed by a plane mirror is virtual and erect.
• The size of the image is the same as the size of the object.
• The image is laterally inverted.
• The image and objects are equidistant from the mirror, which means the distance between the image and mirror is the same as the distance between the mirror and object.

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Uses of Plane Mirror

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• Mirrors are used in our homes to see ourselves.
• Mirrors are mounted inside shopping complexes, and jewelery shops to make the shops appear big.
• Mirrors are also used in solar cookers.
• Mirrors are used in making periscopes, which are used in submarines.
• Mirrors are used in making kaleidoscopes.
• Mirrors are placed at blind turns of the roads, so that drivers can easily see the vehicles coming from the other end.

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Things to Remember

• When the light falls on any object, it bounces back from the object, known as the Reflection of light. All the light falling on the object is not reflected back, the object absorbs a very little amount of light and reflects the rest. The absorption depends on the surface of the object.
• The reflection of light can be classified into three types- Mirror Reflection, Specular Reflection, and Diffuse Reflection.
• The light rays falling on the plane mirror are reflected back, forming an image.
• Law of reflection states that -
  • Angle of Incidence, θi = Angle of Reflection, θr.
  • The Incident ray, Normal, and Reflected ray lie in the same plane.
• The image formed by the plane mirror is virtual, erect, the same size as the object, lateral inverted.
• The image is formed behind the mirror. The image and the object are equi-distant from the mirror.
• Plane mirrors are used in home, jewelry shops and showrooms, solar cookers, manufacturing periscopes, kaleidoscopes, and are placed at blind turns of the roads, to avoid accidents.
• Reflection of Light on Plane Mirror is a topic covered in Unit 6 Optics Chapter 9 Ray Optics and Optical Instruments. According to the revised CBSE Class 12 Physics syllabus, Unit 5 and Unit 6 have a weightage of 18 marks together.

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