A ray diagram for a convex lens is shown below. In this manner, a convex lens is used in :

1. camera
2. cinema
3. burning glass
4. terrestrial telescope

For an object placed at a distance 20 cm in front of a convex lens, the image is at a distance 20 cm behind the lens. The focal length of the convex lens is:

1. 20 cm
2. 10 cm
3. 15 cm
4. 40 cm.

A concave lens forms the image of an object which is:

1. virtual, inverted, and diminished
2. virtual, upright, and diminished
3. virtual, inverted, and enlarged
4. virtual, upright, and enlarged.

For a convex lens when the object is at 2F₁, then image is formed at :

1. F₂
2. 2F₂
3. beyond 2F₂
4. infinity