Sunil Batra Solutions for Chapter: Reflection and Refraction, Exercise 4: Practice Exercise 4D

Find the power (in $\mathrm{D}$) of a concave lens of focal length $3 \mathrm{m}$.

A convex lens is of focal length $30 \mathrm{cm}$. Find the distance where the object should be placed in front of the lens so that the image is formed $10 \mathrm{cm}$ from the lens. What is the magnification?

A convex lens of focal length $18 \mathrm{cm}$ and a concave lens of focal length $24 \mathrm{cm}$ are placed in contact such that they have a common principal axis. Find the power of their combination. Will the combination behave as a converging or diverging lens?

To find the image distance for varying object distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that, he gradually moves the object towards the lens and each time focuses its image on the screen.
What happens to the size of image - does it increase or decrease?

To find the image distance for varying object distances in case of a convex lens, a student obtains on a screen a sharp image of a bright object placed very far from the lens. After that, he gradually moves the object towards the lens and each time focuses its image on the screen.
What happens when he moves the object very close to the lens?

An object of height $4 \mathrm{cm}$ is placed at a distance of $20 \mathrm{cm}$ from a concave lens of focal length $10 \mathrm{cm}$. Use lens formula to determine the position of the image formed.

What is meant by power of a lens? What does its sign ($+$ ve or $-$ve) indicate? State its SI unit. How is it related to the focal length of a lens?

Draw ray diagrams to show the formation of three times magnified (a) real and (b) virtual image of an object by a converging lens. Mark the positions of $O$, $F$ and $2F$ in each diagram.