An object is placed between f and 2f of a convex lens. Which of the following statements correctly describes its image?

A small bulb is placed at the focal point of a converging lens. When the bulb is switched on, the lens produces:

An illuminated object is placed at a distance of 20 cm from a converging lens of focal length 15 cm. The image obtained on the screen is:

Which of the following can make a parallel beam of light when light from a bulb falls on it?

In order to obtain a real image twice the size of the object with a convex lens of focal length 15 cm, the object distance should be: