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 of the screen.

1. In which direction - towards or away from the lens, does he move the screen to focus the object?
2. What happens to the size of the image - does it increase or decrease?
3. What happen when he moves the object very close to the lens?

State two positions in which a concave mirror produces a magnified image of a given object. List two differences between the two images.

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

A large concave mirror has a radius of curvature of 1.5m. A person stands 10m in front of the mirror. Where is the person’s image?

Draw a labelled ray diagram to show how a ray of light is refracted when it passes:

1. From air into an optically denser medium.
2. From an optically denser medium into air.

An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O' of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O', principal focus F and height of the image on the diagram.

Show by drawing a ray-diagram that the image of an object formed by a concave lens is virtual, erect and diminished.

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.

Define:

1. Principal focus of a concave mirror.
2. Focal length of a concave mirror.

Refractive index of diamond with respect to glass is 1.6 and absolute refractive index of glass is 1.5. Find out the absolute refractive index of diamond.