16.A beautiful girl with two normal eyes wants to see full width of her face by a plane mirror. The eye to eye and ear to ear distances of her face are 4 inch and 6 inch respectively. The minimum width of the required mirror is:

17.Two objects (A and B) are 10 cm apart in air. The system is immersed in liquid of refractive index 1.6. The equivalent optical path between A and B will be:

18.In any medium, light travels between two points along a path such that:

19.A thin glass (refractive index 1.5) lens has optical power of -5D in air. Its optical power in a liquid medium with refractive index 1.6 will be:

20.A hair dresser stands with her nose 20 cm in front of a plane mirror. For what distance must she focus her eyes in order to see her nose in the mirror?