What is the absolute refractive index of water?

$A$ beam of light incident on a plane mirror forms a real image on reflection. The incident beam is

The size of an image of an object formed by a mirror with a focal length of $20\, cm$ is observed to be reduced to $1/3^{rd}$ of its size. At what distance is the object placed from the mirror? What is the nature of the image and the mirror?

What happens when an oblique ray of light enters from glass into air?

The figure below shows an object $AB$ placed on the principal axis of a lens $L$. The two foci of the lens are $F_1$ and $F_2$. The image formed by the lens is erect,virtual and diminished. Copy the diagram and answer the following questions: $(i)$ Draw the outline of the lens $(L)$ used. $(ii)$ Draw a ray from $B$ passing through $O$. Show the ray after refraction by the lens. $(iii)$ Draw a ray of light starting from $B$,which after passing parallel to the principal axis,is incident on the lens and emerges after refraction from it. $(iv)$ Locate the final image formed.

$A$ convex mirror used on an automobile has $3\, m$ radius of curvature. If a bus is located at $5\, m$ from this mirror,find the position,nature,and size of the image.