Concave Convex Mirror

Introduction

You may have observed that whenever you stand in front of the mirror, you get an erect, virtual, and same-sized image of yourself. Here, erect means not inverted and virtual image means behind the mirror.

Similarly, the images formed by the concave and convex mirrors have different natures. Some images look erect and some are inverted. Also, it can be a real or a virtual image. While compared according to size, the images formed may be of the same size or enlarged, or small-sized.

In this tutorial, all these natures of images formed by concave and convex mirrors will be discussed in detail. So, let’s get started.

Image Formation Using Ray Diagrams

Firstly, you will need to understand the image formation using ray diagrams. The ray diagrams will make it easier to learn the image of formation.

In a ray diagram, infinite rays of light will emerge from an object placed at some distance from the mirror. An object has an infinite point of the light source and each point radiates a ray of light. However, we will use two rays to understand the ray diagrams in detail. It will be easier as well as neat to understand the diagram quickly with just two rays coming from an object.

Ray Diagrams

Incident ray from an infinite point

Concave Mirror

An incident ray coming from an infinity point that is parallel to the principal axis will be reflected in such a way that it will pass through the Focus (F) point.

Convex Mirror

An incident ray from an infinite point that is parallel to the principal axis will be reflected away from the virtual Focus (F). When the diverged ray will be extended behind the mirror, it will seem to be converging at a virtual Focus (F) point.

Images Coming soon

Image 1: Incident ray from Infinity

Incident ray intersecting Focus (F)

Concave Mirror

When an incident ray intersects the Focus (F) of the concave mirror, it will be reflected parallel to the principal axis.

Convex Mirror

When an incident ray will intersect the virtual Focus (F) of the convex mirror, it will be reflected parallel to the principal axis.

Images Coming soon

Image 2: Incident ray intersects Focus (F)

Incident ray intersecting Centre of Curvature (C):

Concave Mirror

When the incident ray intersects the Centre of Curvature (C), it is reflected on the same path. As a result, the reflected ray overlaps the incident ray and again passes through the Centre of curvature (C).

Convex Mirror

When an incident ray intersects the virtual Centre of Curvature (C), it is reflected on the same path and overlaps the incident ray.

Images Coming soon

Image 3: Incident ray intersects Centre of Curvature (C)

Incident ray at Pole

Concave Mirror

When the incident ray directly incidents at Pole, it gets reflected at the same angle as the angle of incidence ($\angle$i). Here, the law of reflection ($\angle$ i = $\angle$r) holds.

Convex Mirror

Similar to the concave mirror, when an incident ray intersects the Pole (P) of the convex mirror, it gets reflected at an angle the same as the angle of incidence.

Images Coming soon

Image 4: Incident ray at Pole (P)

Now, you may have completely understood the incident ray at different points of the spherical mirrors (concave and convex) and their respective reflected rays. Keeping this concept in mind, let’s learn the image formation by a concave and convex mirror.

Image Formation by A Concave and Convex Mirror

Concave Mirror

 Object at Infinity

When an object is placed at infinity, the image is obtained at the Focus (F). It is real, inverted, and point-sized.

Object beyond Centre of Curvature (C)

If the object is placed beyond the Centre of Curvature (C), the image will be formed between Focus (F) and Centre of Curvature (C). The image will be real, inverted, and small-sized.

Object at Centre of Curvature (C)

When an object is placed at the Centre of Curvature (C), the image will overlap the object at the same point, i.e., Centre of Curvature (C). The image will be real, inverted, and of the same size.

Object placed between Centre of Curvature (C) and Focus (F)

If an object is positioned between the Centre of Curvature (C) and Focus (F), the image will be formed beyond the Centre of Curvature (C). The image formed will be real, inverted, and magnified in nature.

Object at Focus (F)

When the object is at Focus (F), the image will be obtained at the infinity point. That is to say, you will not be able to see the image. It will be a real, inverted, and highly-magnified image.

The object between Focus (F) and Pole (P)

If the object is positioned between the Focus (F) and Pole (P), a virtual image will be formed. That is to say, the image will form behind the mirror. It will be virtual and erect. Also, the image will be magnified.

Images Coming soon

Image 5: Image Formation: Concave Mirror

Convex Mirror

In the case of a convex mirror, there are two actual positions exist outside the mirror which is suitable to position an object. It is because all the points such as Focus, Centre of Curvature, etc. are virtual.

Object at infinity

When an object is placed at infinity, the convex mirror forms a virtual and erect image at virtual Focus (F). The image formed is of point size.

Object between infinity and Pole (P)

When an object is positioned between the infinity point and Pole (P), an erect, small-sized, and a virtual image are formed between virtual Focus (F) and Pole (P)

Images Coming soon

Image 6: Image Formation: Convex Mirror

Conclusion

To recall this tutorial, read this table to briefly understand the image formed by spherical mirrors.

Object Placed	Image Formed	Nature of Image	Image Size
At infinity point	At Focus (F)	Real + Inverted	Point-sized
Beyond Centre of Curvature (C)	In the middle of F and C	Real + Inverted	Small
At Center of Curvature (C)	At Centre of Curvature (C)	Real + Inverted	Same-sized
Between Centre of Curvature (C) & Focus (F)	Beyond C	Real + Inverted	Magnified
At Focus (F)	At infinity point	Real + Inverted	Highly Magnified
Between Focus (F) and Pole (P)	Behind the mirror	Virtual + Erect	Magnified

Table 1. Concave Mirror

Object Placed	Image Formed	Nature of Image	Image Size
At infinity point	At virtual Focus (F)	Virtual + Erect	Point-sized
Between infinity and Pole (P)	Between virtual Focus (F) and Pole (P)	Virtual + Erect	Small

Table 2. Convex Mirror

FAQs

Q1. What are the two types of images formed by spherical mirrors?

The image formed by spherical mirrors can be real/virtual and erect/inverted.

Q2. What is meant by erect image?

An erect image means an image that is in the same direction as an object. In other words, an image has a right-side-up.

Q3. What is the erect and inverted image?

An inverted image is an image formed that is upside down whereas an erect image is the same as an object.

Q4. What is called a virtual image?

An image that forms behind the mirror is called a virtual image.