Concave and Convex Mirrors: Overview, Questions, Preparation

Updated on Aug 27, 2021 02:03 IST

Table of content

Concave and Convex mirrors
Image formation by Spherical Mirrors
Concave
Convex
Illustrative Examples

Concave and Convex mirrors

Plane Mirrors

This type of a mirror is a plane reflecting surface. The size of the image formed is almost equal to the size of the object.

Spherical Mirrors

These mirrors have curved surfaces. The spherical mirrors are of two types:

Convex Mirrors
Concave Mirrors

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

The concave mirror is a spherical mirror whose reflecting surface is curved inwards (faces the centre of the sphere). On the other hand, a convex mirror has an outward-reflecting surface.

Image formation by Spherical Mirrors

The following ray diagrams show the various image formations for both the spherical mirrors.

Concave

Object Position	Image Position	Image Size	Image Nature
At infinity	At the focus F	Highly diminished, point size	Real and inverted

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

Object Position	Image Position	Image Size	Image Nature
Beyond C	Between F and C	Diminished	Real and inverted

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

Object Position	Image Position	Image Size	Image Nature
At C	At C	Same size	Real and inverted

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

Object Position	Image Position	Image Size	Image Nature
Between C and F	Beyond C	Enlarged	Real and inverted

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

Object Position	Image Position	Image Size	Image Nature
At F	At infinity	Highly enlarged	Real and inverted

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

Object Position	Image Position	Image Size	Image Nature
Between P and F	Behind the mirror	Enlarged	Virtual and erect

(Image source:https://ncert.nic.in/ncerts/l/jesc110.pdf)

Convex

Object Position	Image Position	Image Size	Image Nature
At infinity	At F, behind the mirror.	Highly diminished, point size	Virtual and erect

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

Object Position	Image Position	Image Size	Image Nature
Between infinity and P	Between P and F, behind the mirror.	Diminished.	Virtual and erect

(Image source: https://ncert.nic.in/ncerts/l/jesc110.pdf)

‘Convex and Concave Mirrors’ is a topic from the chapter ‘ Light- Reflection and Refraction’, taught in Class X Science (NCERT). 4 questions for 8 marks are asked in the exam from this chapter.

Illustrative Examples

Example 1: A convex mirror has a radius of curvature of 6.00m. If a tree is at 10.00m from this convex mirror, find the nature, position, and size of the image of the tree.

Solution: Radius of curvature, R=+6.00m;

Object-distance, u=–10.00m;

Image-distance, v=?

Height of the image, h′=?

Focal length, f=R/2=+6.00m/2=+3.00m

Since 1/u+1/v=1/f,

Thus, v=uf/(f-u)=30/13=+2.31 m

And, m=h'/h=-v/u=2.31/10.00=0.23.

Therefore, the image is virtual, erect, and smaller in size by a factor of 0.23.

Example 2: Given h=4cm, u=-25cm, f=-15cm. Find v and h'?

Solution: Since 1/u+1/v=1/f,

1/v=1/25-1/15

v=-37.5cm

m=h'/h=-v/u

h'=-vh/u.

h'=-6cm.

Example 3: h=4cm, h’=16cm, u=-10cm, v=?

Solution: h'/h=-v/u

16/4=v/10

v=40cm.

FAQs

Q: What is reflection?

A: The phenomenon of light when it bounces off shiny and polished surfaces is called reflection.

Q: What are the types of mirrors?

A: Plane mirrors and spherical mirrors.

Q: What are the types of spherical mirrors?

A: Concave and convex.

Q: Define Concave and Convex mirrors.

A: The concave mirror is a spherical mirror whose reflecting surface is curved inwards. The reflecting surface of the convex mirror is curved outwards.

Q: What is the mirror formula?

A: 1/u+1/v=1/f; where u=object distance, v=image distance, f=focal length.