A lamp placed 70.0 cm from a screen on one side produces the same illumination as a standard 60 cd lamp placed 105 cm away on the other side of the screen. What is the luminous intensity of the first lamp ?

An object placed at 20 cm from a lens, forms an image on a screen placed 60 cm on the other side of the lens. What is the focal length and type of the lens ?

An intensity of illumination of 4 flux is required at a distance of 5m from an electric lamp. What must be the luminous intensity of the lamp?

A 16 cd lamp placed at a distance of 125 cm from a screen produces the same illuminance on the screen as that produced by a bulb placed at a distance of 175 cm from the scree. If the bulb takes 0.85 A current at 110, find its efficiency.

A needle placed 45cm from a lens forms an image on the screen placed 90cm on the other side of the lens. What is the type of lens ? Find the focal length. If the length of needle is 5cm. What is the length of image ?

An index pin of height 3 cm is kept at a distance of 15 cm from a convex lens of focal length 10 cm. The image is obtained on a screen placed on the other side of the lens. What is the height and nature of the image ?

Two small lamps A and B the first placed at 0.6m to the left of a translucent screen and the second placed at 1m to the right of the screen produced equal illumination on both sides of the screen. A third lamp of the same luminous intensity as that of A is kept to the left of A at a distance of 0.4m from A. By what distance the source B should be moved to produce equal illumination again ?

A candle placed 25 cm from a lens forms an image on a screen placed 75 cm on the other side of the lens. The focal length and type of the lens should be

A needle placed at 30 cm from the lens forms an image on a screen placed 60 cm on the other side of the lens. Identify the type of lens and determine the focal length.