Concepts

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

For a Concave lens,

There are only 2 cases

They are

• Object is Placed at Infinity
• Object is Placed between Infinity and Optical Center

## Case 1 - Object is Placed at infinity

In this Case, Object 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 refraction

Hence, Image is formed at Focus

And it is on the left side of the lens. So, Image is virtual

And it is very very small

We can say that

• Image is virtual (left side of the lens)
• Image is Erect
• Image is Smaller than the Object (Highly Diminished)

## Case 2 - Object is between Infinity and Optical Center

Here, Object AB kept anywhere on the principal axis - between Infinity and Optical Center (O)

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 Optical Center

So, the ray will go through without any deviation

Where both reflected rays meet is point A'

And the image formed is A'B'

This image is formed between F 1 and Optical Center (O)

We can say that

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

To summarise

 Position of the object Position of the image Relative size of the image Nature of the image At infinity At focus F 1 Highly diminished, Point - Sized Virtual and erect Between infinity and optical centre O of the lens Between focus F 1 and optical centre O Diminished Virtual and erect

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