A small object is so placed in front of a convex lens of 5 cm focal length that a virtual image is formed at a distance of 20 cm. Find the magnification.

State and explain the New Cartesian Sign Convention for spherical lenses.

An object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image. Draw the diagram to represent the position.

Find the position and nature of the image of an object 8 cm high and 10 cm in front of a convex lens of focal length 6 cm.

Calculate the focal length of a convex lens which produces a virtual image at a distance of 60 cm of an object placed 20 cm in front of it.