Mirror

A mirror is a smooth and polished reflecting surface. It forms an image by reflection of light.

Mirrors are mainly of two types

Plane Mirror

Spherical Mirror

Spherical Mirror

A mirror whose reflecting surface is a part of a sphere is called a spherical mirror. Spherical mirrors are of two types: concave mirror and convex mirror.

Plane Mirror

A mirror whose reflecting surface is flat is called a plane mirror.

Plane Mirror

A plane mirror has a flat reflecting surface.

Characteristics of the Image Formed by a Plane Mirror

⭐ The image is virtual.

⭐ The image is erect.

⭐ The image is of the same size as the object.

⭐ The image is formed behind the mirror.

⭐ The distance of the image from the mirror is equal to the distance of the object from the mirror.

⭐ The image shows lateral inversion.

Lateral Inversion

In a plane mirror, the left side of an object appears as the right side of the image, and the right side appears as the left side of the image. This apparent left-right reversal is called lateral inversion.

Actually, a plane mirror does not truly interchange left and right. It reverses the front-back direction. Our brain interprets this as a left-right change.

Features of Lateral Inversion

⭐ It is seen in images formed by a plane mirror.

⭐ The image remains erect and of the same size.

⭐ Left and right appear reversed.

⭐ The top and bottom do not get reversed.

Why is AMBULANCE written in reverse?

The word AMBULANCE is written in reverse on the front of an ambulance. When a driver sees it in the rear-view mirror, lateral inversion makes the word appear correct. This helps the driver identify the ambulance quickly and give way.

Number of Images Formed by Two Plane Mirrors

If two plane mirrors are inclined at an angle , the number of images depends on the value of .

Let x = .

Rule 1: If x is an even integer

The number of images is:

Rule 2: If x is an odd integer

If the object is placed symmetrically between the two mirrors, then:

If the object is not placed symmetrically, then:

Rule 3: If x is not an integer

The number of images is the greatest integer less than x.

Rule 4: If the two mirrors are parallel

If the two mirrors are parallel, the number of images is infinite.

Periscope

A periscope is an optical instrument used to see objects that are not in the direct line of sight. It is commonly used in submarines and by soldiers.

Structure of a Periscope

A simple periscope has two plane mirrors placed parallel to each other at an angle of 45° to the tube.

Working of a Periscope

Light from the object falls on the upper mirror. It is reflected downwards to the lower mirror. The lower mirror reflects the light into the eye of the observer.

Uses of a Periscope

⭐ In submarines to see objects above the water surface.

⭐ By soldiers to observe from behind a wall or trench.

⭐ In simple science models to understand reflection.

Kaleidoscope

A kaleidoscope is an optical toy that forms beautiful colourful patterns by multiple reflection.

Structure of a Kaleidoscope

It usually has three plane mirrors placed at angles inside a tube. Small coloured glass pieces are placed at one end.

Working of a Kaleidoscope

Light enters the tube and reflects many times between the mirrors. Due to multiple reflection, different colourful patterns are formed.

Quick Revision

⭐ A mirror is a smooth reflecting surface.

⭐ A plane mirror has a flat reflecting surface.

⭐ The image in a plane mirror is virtual, erect and of the same size as the object.

⭐ Lateral inversion means apparent left-right reversal.

⭐ Two inclined plane mirrors can form multiple images.

⭐ A periscope works by reflection from two mirrors.

⭐ A kaleidoscope works by multiple reflection.

Common Mistakes