Image formed by Plane Mirror

‘Image formed by Plane Mirror‘ is an important topic in general science. For upcoming competitive exams like SSC, Banking, UPSC, Railways, and State Level Exams, general science is vital. To cover all general science topics, we divided each chapter into several subtopics. The topic ‘Image formed by Plane Mirror ‘ comes under the Ray Optics of Physics chapter.

What is a Mirror?

• A Mirror is a light-reflecting, polished surface glass.
• A mirror reflects almost all light that is incident on it.
• The polished surface of the glass is coated with a reflective layer.

Coating of Mirrors

• Applying a thin layer of metal (reflective layer) on one surface of a glass is known as a coating of the mirror.

• Metal plating techniques are used to give a thin coating to the metal.

• Metals used in Coating
• Silver
• Aluminum
• Gold
• Zinc
• Copper
• Platinum
• Tin

• Among the above list, silver and aluminium are the most common and widely used metals for coating mirrors.

Silvering of Mirrors

◘ Silvering of Mirrors is a process in which a thin layer of silver is applied on the surface of a glass so that most of the incident light on it can be reflected.

◘ Glucose is used in the silvering of mirrors.

Types of Mirror

• Based on the shape a mirror is classified into two types, namely____
1. Plane mirror
2. Spherical mirror

Plane Mirror

• When the reflecting surface of a mirror is flat (not curved), it is called a plane mirror.

Properties of Plane mirror

• In the case of a plane mirror, the angle of reflection and the angle of incidence are equal.

• An image formed by a plane mirror is always virtual and erect.
• And the size of the image is equal in size to the object.

• The distance between the image from the mirror and the distance between the object from the mirror are equal.

• Linear magnification produced by a plane mirror is 1.

• The minimum size of the mirror required to see the full image of an object is half of the object’s height.
• Focal length of plane mirrors in infinity. (that means Power is Zero)

Characteristics of the image formed by a plane mirror

• A plane mirror formed an erect (Upright), virtual image.
• And the size of the image is the same as the object

• The image formed by a plane mirror is at the same distance inside the mirror as the object in front of it.

• In the below image, OC = CD
• ‘OC’ is the distance between the object and the mirror and CD is the distance between the image and the mirror.

• In order to view an object’s entire image, the plane mirror’s minimum length should be half of the object’s length.

• For example, If your height is 5 feet and you want to see your full image in a plane mirror, then the length of the mirror should be 5/2 or 2.5 feet.

The image is formed by two Plane Mirrors placed at a certain angle

◘ When two plane mirrors are facing each other at an angle θ an object is placed between them, and then

1. The number of images formed by two plane mirrors is:
▲ (No. of Images) n = (m -1)  [Here, m = 360⁰ / θ]
★ If m is even
★ OR, the object lies symmetrically.

2. The number of images formed by the mirrors is:
▲ (No. of Images) n = m  [m = 360⁰ / θ]
★ If 360⁰ / θ is odd
★ OR, the object lies asymmetrically.

▲ Let’s Simplified the formula –
• At first calculate the value of m = (360⁰ / θ)

✪ If m is even, then (m -1) is the total number of images, irrespective of the position of the objects. (Symmetrical or Unsymmetrical)

✪ If m is odd then consider the following 2 cases.
◘ Case I
• If the object is placed symmetrically then (m-1) is the actual number (n) of images.

◘ Case II
• If the object is placed asymmetrically then n itself is the number (n=m) of images.

❖ Numerical Example-
• Suppose two plane mirrors are perpendicular to each other or the angle between them is 90⁰.

• The number of images formed by the mirrors is __

• The Value of m = 360/90 = 4
• 4 is an even number, so the actual number of images is (4-1) =3

• Suppose the angle between two plane mirrors is 72⁰

• The number of images formed by the mirrors is 5.

• Value of m = 360/72 = 5
• 5 is an odd number, so the actual number of images _

• n = (m – 1) = (5 – 1) = 4
• If the object is placed symmetrically

• n = 5 (n=m)
• If the object is placed asymmetrically

▲ Note –
◘ Two parallel plane mirrors form infinite numbers of images if the angle (θ) between them is 180 degrees and they face each other like the image below.

• Two parallel plane mirrors form only 2 images if the angle (θ) between them is 180 degrees and they face each other like the following image.

• Two parallel plane mirrors formed only 2 images if they are perpendicular to each other or the angle (θ) between them is 90 degrees and they are facing each other like the following image.

Spherical Mirror

• A spherical mirror is the small cut-out portion, of a reflecting sphere.
• There are two types of spherical mirrors
1. Concave
2. Convex

Concave mirror
• The spherical mirror whose inner surface is a reflecting surface and the outer surface is polished, is called a concave mirror.

• Another name for a concave mirror is a converging mirror because it converges light rays after reflection (light rays converge to a point).

Convex mirror
• The spherical mirror whose outer surface is a reflecting surface and the inner surface is polished, is called a convex mirror.

• Another name for the convex mirror is a diverging mirror because it generally diverges (separates the rays of light from another) the beam of light after reflection.

Use of Mirror

Plane mirror: Some common uses of plane mirrors are:
• As a looking glass.
• Used in torch lights.
• Used in solar cookers.
• Used in constructing periscope. (2 plane mirror is used)
• Used in making kaleidoscope toys.

• The Kaleidoscope is an optical instrument that produces beautiful colour patterns.
• It has two or more reflecting surfaces which are placed at such an angle so that they can produce multiple symmetrical patterns.

Uses of Concave Mirror: Some of the common uses of concave mirrors are:
• Searchlights
• Shaving mirrors
• makeup mirrors
• Satellite dishes
• Headlights of vehicles
• dental mirrors

Convex mirror: Convex mirrors are commonly used in:
• Rear view mirror in vehicles.
• Used as a Security mirror in shops
• Used in interior design

◘ Convex mirrors provide a much wider view angle than plane mirrors.

Frequently Asked Questions (FAQ)

For PDF, Print this page and save as a PDF
Click the “Print This Page Button”

Print this Page