For a concave mirror,if the object distance $u = \infty$,then the image distance $v = ..........$.

$(a)$ Water has a refractive index of $1.33$ and alcohol has a refractive index of $1.36$. Which of the two media is optically denser? Give a reason for your answer. Draw a ray diagram to show the path of a ray of light passing obliquely from water to alcohol.
$(b)$ The absolute refractive index of diamond is $2.42$ and the absolute refractive index of glass is $1.50$. Find the refractive index of diamond with respect to glass.

Which type of reflection will be represented by light reflected from a book?

If an object is placed symmetrically between two plane mirrors, inclined at an angle of $72^{\circ},$ then the total number of images formed is

$A$ concave mirror and a convex lens are held in water. What changes, if any, do you expect in their focal length?

Where should an object be placed in front of a concave mirror to obtain an inverted and magnified image?