Explain how to read the following message which was found on some blotting paper:

What is meant by:
Draw diagram to show the action of convex mirror on a beam of parallel light rays. Mark on this diagram principal axis, focus F, centre of curvature C, pole P and focal length ƒ, of the convex mirror.

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?

An extended object in the form of an arrow pointing upward has been placed in front of plane mirror. Draw a labelled ray-diagram to show the formation of its image.

A convex lens is immersed in a liquid of refractive index greater than that of glass. How will the nature of lens change?

How could you find the focal length of a convex lens rapidly but approximately?

“A concave mirror of focal length ‘f’ can form a magnified erect as well as an inverted image of an object placed in front of it.” Justify this statement stating the position of the object with respect to the mirror in each case for obtaining these images.

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12cm.
Where will the image of this object be, if it is placed 24cm in front of the mirror? Draw ray diagram for this situation also to justify your answer.
Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.

Where must the object be placed for the image formed by a converging lens to be:

1. Real, inverted and smaller than the object?
2. Real, inverted and same size as the object?
3. Real, inverted and larger than the object?
4. Virtual, upright and larger than the object?

Your eye contains a convex lens. Why is it unwise to look at the sun?