An optical device has been given to a student and he determines its focal length by focusing the image of a sun on a screen placed 24 cm from the device on the same side of the sun.(a) Name the optical device(b) Find its focal length

The light source is 0.27 m from the lens. The screen is moved to a distance of 0.11 m from the centre of the lens so an image of the light source is seen at the screen.Calculate the focal length of the lens. Express answer to three decimal places,use SI units.

An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens upto two places of decimal.

A projector lens is needed to form an image on a screen 10 times the size of its corresponding object. The screen is located 8.0 m from the lens. What is the required focal length of the lens?(Watch out for the direction of the image from a converging lens)Question 3

Define the following :(i) Focal length.(ii) Principal focus

Define the focal length of a lens.The distance to the furthest object that can be seen through itThe minimum thicknessThe distance from the focal point to the centre of the lensIts distance from an observer's eye