For driving a car,what type of mirror would you prefer to see the traffic at your back?

The figure below shows an object $AB$ placed on the principal axis of a convex lens placed in air. $F_{1}$ and $F_{2}$ are the two foci of the lens. Copy the diagram.
$(i)$ Draw a ray of light starting from $B$ and passing through $O$. Show the same ray after refraction by the lens.
$(ii)$ Draw another ray from $B$ which passes through $F_{2}$ after refraction by the lens.
$(iii)$ Locate the final image formed.
$(iv)$ Is the image real or virtual?

The refractive indices of turpentine oil,kerosene,and alcohol are $1.47, 1.44$,and $1.36$ respectively. Based on this information,complete the following ray diagrams to show the path of a ray of light through each medium. (Give a reason for your answer.)

Where is the object placed in a compound microscope?

$A$ convex lens of focal length $20 \, cm$ can produce a magnified virtual as well as real image. Is this a correct statement? If yes,where shall the object be placed in each case for obtaining these images?

Two lenses of power $+3.5 D$ and $-2.5 D$ are placed in contact. Find the power and focal length of the lens combination.