An illuminated object and a screen are placed `90 cm` apart. What is the focal length and nature of the lens required to produce a clear image on the screen twice the size of the object ?

A source of light and a screen are placed 90 cm apart. Where should a convex lens of 20 cm focal length be placed in order to form a real image of the source on the screen ?

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

An object and a screen are placed 80 cm apart. There are two positions at which a convex lens forms a real image on the screen, the magnification in the cases being 3/2 and 2/3. Calculate the focal length of the lens.

Aluminous object and a screen are placed on an optical bench and a converging lens is placed between them to throw a sharp image of the object on the screen, the linear magnification of the image is found to be 2.5. The lens is now moved 30 cm nearer the screen and a sharp image is again formed. Calculate the focal length of the lens.

An object and a screen are fixed at a distance d apart. When a lens of focal length f is moved between the object and the screen, sharp images of the object are formed on the screen for two positions of the lens. The magnifications produced at these two positions are M_(1) "and" M_(2) -

The distance between the object and the screen is d (greater than 4 times the focal length of a convex lens). Real images of the object are obtained on the screen for two positions of the lens that are separated by distance x apart. The ratio of size of the images in the two positions of the lens are

(a) A screen is kept at a distance of 1m from the object. A converging lens between the object and the screen, when placed at any of the two positions which are 60cm apart, forms a sharp image of the object on the screen. Find the focal length of the lens. (b) In the two positions of the lens, lateral size of the image is 4cm and 9cm. Find the size of the object.

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: