Concepts

Class 10
Chapter 10 Class 10 - Light - Reflection and Refraction

For a Convex Mirror,

The focus and center of curvature is on the right side of the mirror

So, there will only be 2 cases.

They are

• Object is Placed at Infinity
• Object is Placed between Principal axis and Infinity

## Case 1 - Object is Placed at infinity

In this Case, Object AB is kept far away from mirror (almost at infinite distance)

So, we draw rays parallel to principal axis

Since ray parallel to principal axis appear to pass through the Focus

All rays appear to meet at focus after reflection

Hence, Image is formed at Focus

And it is on the other side of the mirror. So, Image is virtual

And it is very very small

We can say that

• Image is behind the Mirror (Virtual Image)
• Image is Erect
• Image is Smaller than the Object (Highly Diminished)

## Case 2 - Object is between Infinity and Pole (P)

Here, Object AB kept anywhere on the principal axis - between Infinity and Pole (P)

First, we draw a ray parallel to principal axis

So, it appears to pass through focus after reflection

We draw another ray which passes through Center of Curvature

So, the ray will go back along the same path after reflection

Where both reflected rays meet is point A'

And the image formed is A'B'

This image is formed between Pole (P) and Focus (F)

We can say that

• Image is behind the Mirror (Virtual Image)
• Image is Erect
• Image is Smaller than the Object (Diminished)

## To summarise

 Position of the object Position of the image Size of the image Nature of the image At infinity At the focus F, behind the mirror Highly diminished, point-sized Virtual and erect Between infinity and the pole P of the mirror Between P and F, behind the mirror Diminished Virtual and erect

## Questions

NCERT Question 3 - Where should an object be placed in front of a convex lens to get a real image of the size of the object?

(a) At the principal focus of the lens

(b) At twice the focal length

(c) At infinity

(d) Between the optical centre of the lens and its principal focus.

NCERT Question 5 - No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be

(a) only plane.

(b) only concave.

(c) only convex.

(d) either plane or convex

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#### Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo