A screen is placed a distance 40 cm away from an illuminated object. A converging lens is palced between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens

A luminous object is placed at a distance of 40 cm from a converging lens of focal length 25 cm. The image obtained in the screen is

A luminous object is separated from a screen by distance d. A convex lens is placed between the object and the screen such that it forms a distinct image on the screen. The maximum possible focal length of this convex lens is

A source of light is located at a disatnce l = 90 cm from a screen. A thin converging lens provides the sharp image of the source when placed between the source of light and the screen at two positions. Determine the focal length o fthe lens if (a) the distance between the two positions of the lens is Delta l = 30 cm , (b) the transverse diamensions of the image at one position o fthe lens are eta = 4.0 greater than those at the pther position.

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:

A convex lens forms a real image on a screen placed at a distance 60 cm from the object. When the lens is shifted towards the screen by 20 cm , another image of the object is formed on the screen. The focal length of the lens is :

A luminous object and a screen are at a fixed distance D apart. A converging lens of focal length f is placed between the object and screen. A real image of the object in formed on the screen for two lens positins if they are separated by a distance d equal to