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?

If an object is placed at a distance of 8cm from a concave mirror of focal length 10cm, discuss the nature of the image formed by drawing the ray diagram.

Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray of light parallel to the principal axis of a convex mirror and show the angle of incidence and angle of reflection on it.

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?

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

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

Why does a driver prefer to use a convex mirror as a rear-view mirror in a vehicle?

Three convex lenses are available having focal lengths of 4cm, 40cm and 4m respectively. Which one would you choose as a magnifying glass and why?

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.