A 5.0 diopter lens forms a virtual image which is 4 times the object placed perpendicularly on the principal axis of the lens. Find the distance of the object from the lens.

A pin of length 2.0 cm lies along the principal axis of a converging lens, the center being at a distance of 11 cm from the lens. The focal length of the lens is 6 cm. Find the size of the image.

The diameter of the sun is 1.4 x 10⁹ m and its distance from the earth is 1.5 x 10¹¹ m. Find the radius of the image of the sun formed by a lens of focal length 20 cm.

A diverging lens of focal length 20 cm and a diverging mirror of focal length 7.5 cm are placed 5.0 cm apart with their principal axes coinciding. Where should an object be placed so that its image falls on itself?

A converging lens of focal length 12 cm and a diverging mirror of focal length 7.5 cm are placed 5 cm apart with their principal axis coinciding. Where should an object be placed so that the image would fall on itself?