The lens of a 35 mm camera has a focal length of 56 cm.
Find its f-number if the diameter of the lens si 20 cm.

If the focal length of a converging lens is 50 cm. What is the power of the Lens ?

An astronomical telescope has an objective lens of focal length 20 m and eyepiece of focal length 1 cm. Find the angular magnification of the telescope.

An object of size 5 cm is placed at distance of 25 cm in front of a convex lens of focal length 20 cm. Find the size and nature of image and its distance from the lens.

Power of a lens is -5d, its focal length is:

A concave lens has focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens.

A biconvex lens of focal length 15 cm is in front of a plane mirror.The distnace betweent the lens and the mirror is 10 cm.A small object is kept at a distance of 30 cm from the lens .The final image is

A converging lens has a focal length of 20 cm in air. It is made of a material of refractive index 1.6. If it is immersed in a liquid of refractive index 1.3, what will be the new focal length? How does the nature of the lens change. If this lens is immersed is a liquid of refractive index 1.8 ?

A convex lens of focal lenth 30 cm and a concave lens of focal length 60 cm are placed in contact.Find the power of the combination.

The radii of curvature of the faces of a double convex lens are 20 cm and 30 cm. Its focal length is 24 cm. What is the refractive index of the glass?