Write the formula for a lens connecting image distance (υ), object distance (u) and the focal length (f). How does the lens formula differ from the mirror formula?

A pencil when dipped in water in a glass tumbler appears to be bent at the interface of air and water. Will the pencil appear to be bent to the same extent, if instead of water we use liquids like, kerosene or turpentine. Support your answer with reason.

Show the lateral displacement of the ray on the diagram.

A boy with a mouth 5cm wide stands 2m away from a plane mirror. Where is his image and how wide is the image of his mouth?

State and define the S.I. unit of power of a lens.

Which lens would you prefer to use while reading small letters from a dictionary?

Identify the device used as a spherical mirror or lens in following cases, when the image formed is virtual and erect in each case.Object is placed between the focus and device, image formed is enlarged and on the same side as that of the object.

To find the image distance for varying object distances in case of a convex lens of focal length 15 cm, a student obtains on a screen a sharp image of a bright object by placing it at 20 cm distance from the lens. After that he gradually moves the object away from the lens and each time focuses the image on the screen.

1. In which direction-towards or away from the lens does he move the screen to focus the object?
2. How does the size of image change?
3. Approximately at what distance does he obtain the image of magnification -1?
4. How does the intensity of image change as the object moves farther and farther away from the lens?

Draw ray diagrams showing the image formation by a convex mirror when an object is placed:
At infinity.

With the help of a ray diagram explain why a concave lens diverges the rays of a parallel beam of light.