1) An astronomer uses a converging lens to observe the moon. If the focal length of the lens in the telescope is 20 cm, what is the distance from the observer's eye to the lens in the telescope to see a clear image of the moon?

2) A converging lens has a focal length of 20.0 cm. If  an object is placed 50.0 cm from the optical centre of the lens, how far will the image be from the optical centre of the lens?

3) The following diagram shows an object O, placed next to a lens as shown below:

At which position is the image likely to be found?

4) When an object is placed 31 cm from a lens the image formed is real, inverted and diminished. When the object is placed 29 cm from the lens the image formed is real, inverted and enlarged. Which of the following is a possible focal length of the lens?

5) An object O is placed at a distance of 5.0 cm from a convex lens. The diagram shows the paths of three rays from the object O through the lens.

Which of the following statements is correct?