‘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 a vital subject. To cover all the topics of general science, we divided each chapter into several subtopics. The topic ‘Image formed by Plane Mirror ‘ comes under the chapter Ray optics of Physics.
What is 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
• Among the above list Silver and Aluminium are the most common and widely used metal in coating of mirrors.
Silvering of Mirrors
◘ Silvering of Mirrors is a process in which a thin layer of silver applied on a 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
• When the reflecting surface of a mirror is flat (not curved) then 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 both 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 height of the object.
• Focal length of plane mirrors in infinity. (that means Power is Zero)
Characteristics of image formed by 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 is in front of it.
• In the below image OC = CD
• ‘OC’ is the distance between the object and mirror and CD is the distance between the image and the mirror.
• In order to view the entire image of an object the minimum length of the plane mirror should be half of the length of the object.
• 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.
Image formed by two Plane Mirror placed at a certain angle
◘ When two plane mirror is facing each other at an angle θ an object is placed between them, then
1. 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. 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 formed infinite numbers of images if the angle (θ) between them is 180 degrees and they are facing each other like the below image.
• Two parallel plane mirrors formed only 2 images if the angle (θ) between them is 180 degrees and they are facing 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.
• A spherical mirror is the small cut-out portion, of a reflecting sphere.
• There are two types of spherical mirrors
• 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).
• 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 color patterns.
• It has two or more reflecting surface which is 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:
• Shaving mirrors
• makeup mirrors
• Satellite dishes
• Headlight 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 mirror provides a much wider angle of view compared to plane mirrors.
Frequently Asked Questions (FAQ)
Answer: Erect, Virtual Image
Answer: 2 Plane Mirror
Answer: Concave mirror
Answer: Convex Mirror
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