Image Formation By Concave Mirror: Overview, Ray Diagrams, Mechanism

A spherical mirror whose inner surface is reflected is known as a Concave Mirror. A concave mirror produces both real and virtual images. Based on the distance between the concave mirror and the object, the concave mirror displays real or virtual images. The image formation by concave mirrors is represented in the form of ray diagrams.

When the object is placed very close to the concave mirror, then the images will get magnified and give a virtual image. When the same object’s distance is increased from the mirror, the concave mirror produces a real image. In this article, we have provided all the necessary information about rules for image formation of concave mirrors with ray diagrams. Read on to find out more.

Image Formation By Concave Mirror: Overview

Before understanding what type of images is formed by a concave mirror, let’s go through some of the important terms:

1. Pole: Pole is usually denoted as P. Pole is the centre of reflecting surface of a spherical mirror.
2. Centre of Curvature: The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre and this is known as Centre of Curvature. The centre of curvature is denoted by C. In a concave mirror, Centre of Curvature lies in front of the mirror.
3. Radius of Curvature: The radius of the sphere of which the reflecting surface of a spherical mirror is called the radius of curvature. The radius of curvature is denoted as R. The distance between the Pole and Centre of Curvature will be equal to the Radius.
4. Principal Axis: A straight line which is passing through the Pole (P) and the Centre of Curvature (C) is known as Principal Axis.
5. Principal Focus: The principal focus is denoted by F. The parallel rays which are reflected by the concave mirror are falling on the principal axis at one common point. This point is called principal focus or F.
6. Focal Length: The distance between pole (P) and the principal axis is known as focal length.

Concave Mirror: Ray Diagram

With the help of Ray Diagrams we can understand how images are formed in concave mirrors. We should consider at least 2 incident rays coming from an object to understand the image formation in Concave mirrors. The intersection of 2 rays after reflection provides the image position of an object.

In concave mirrors, there are 4 ray diagrams through which an image of the object can be located. The four ray diagrams of concave mirrors are given below:

• (i) A ray parallel to the principal axis, after reflection, will pass through the principal focus (F).

• (ii) A ray passing through the principal axis, after reflection, will emerge parallel to the principal axis.

• (iii) A ray passing through the centre of curvature (C), after reflection, is reflected back along the same path.

• (iv) A ray incident obliquely (diagonally) to the principal axis, towards the Pole (P), is reflected obliquely.

In all the above 4 cases, the laws of reflection are followed which means “at the point of incidence, the incident ray is reflected in such a way that the angle of reflection equals the angle of incidence.”

Concave Mirror Image Formation

When two rays converge at a point real image forms in the concave mirror. But if the rays do not meet but diverge from a point then it forms a virtual image. There are 6 different positions in which an object can be placed in the front of the Concave mirror and they are

• (a) When the object is placed at infinite, it gives a highly diminished, point-size real image

• (b) When the object is placed beyond the center of the curvature, it forms a diminished, real and inverted image

• (c) When the object is exactly placed at the curvature, then the image would be the same size as the object.

• (d)  When the object is placed between the principal focus and center of the curvature, then the image would be larger than the object and the image would be real and inverted.

• (e) When the object is placed at the principal focus, then a highly enlarged inverted image will be formed.

• (f) When the object is placed between the pole and principal focus. The image would be virtual, erect, and display larger than the object.

Summary of Concave Mirror Image Formation

The summary of concave mirror image formation is given below:

FAQs on Image Formation By Concave Mirror

Q.1. What are the 6 cases of a concave mirror?
A. The 6 cases of Concave mirror are given below:
a. When the object is placed at infinite
b. When the object is placed beyond the centre of the curvature
c. When the object is exactly placed at the curvature
d. When the object is placed between principal focus and centre of the curvature
e. When the object is placed at the principal focus
f. When the object is placed between the pole and principal focus

Q.2. Between which two points of the concave mirror should an object be placed to obtain a magnification?
A. We should place the object between focus and centre of curvature to obtain the magnified image.

Q.3. What is C in the concave mirror?
A. C denotes Centre of Curvature in a concave mirror. The centre of the sphere formed by the reflecting part of a spherical mirror is called the centre of curvature.

Q.4. What type of image is formed by a concave mirror?
A. Concave mirror forms both Virtual or Real images based on the distance between the object and the mirror.

Q.5. What type of image is formed by a concave mirror?
A. Concave mirror forms both Virtual or Real images based on the distance between the object and the mirror.

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