A convex lens of focal length 25cm and a concave lens of focal length 10cm are placed in close focal contact with each other. Calculate the lens power of this combination.

When a fork is seen through lenses A and B one by one, it appears as shown in the diagrams. What is the nature of (i) lens A, and (ii) lens B? Give reason for your answer.

Which of the following diagrams shows the ray of light refracted correctly?

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

A star appears slightly higher (above) than its actual position in the sky illustrate it with the help of a labelled diagram.

A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that he moves gradually the flame towards the lens and each time focuses its image on the screen.

1. In which direction does he move the lens to focus the flame on the screen?
2. What happens to the size of the image of the flame formed on the screen?
3. What difference is seen in the intensity (brightness) of the image of the flame on the screen?
4. What is seen on the screen when the flame is very close (at about 5 cm) to the lens?

A 4 cm tall object is placed on the principal axis of a convex lens. The distance of the object from the optical centre of the lens is 12cm and its sharp image is formed at a distance of 24cm from it on a screen on the other side of the lens. If the object is now moved a little away from the lens, in which way (towards the lens or away from the lens) will he have to move the screen to get a sharp image of the object on it again? How will the magnification of the image be affected?

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.

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

With the help of a labelled diagram explain how a convex lens converges a beam of parallel light rays.