$A$ virtual,magnified and erect image can be formed by a concave mirror.

Which of the following always form a virtual image?

$(a)$ Define absolute refractive index.
$(b)$ The path of a light ray from three different media $A, B$ and $C$ for a given angle of incidence is shown below. Study the diagrams and answer the following questions.
$(i)$ Which of the three media $A, B$ or $C$ has maximum optical density?
$(ii)$ Through which of the three media,will the speed of light be maximum?
$(iii)$ Will the light travelling from $A$ to $B$ bend towards or away from the normal?
$(iv)$ Will the refractive index of $B$ relative to $C$ be more than unity or less than unity?

What type of lens behaviour will an air bubble inside water show?

Both a spherical mirror and a thin spherical lens have a focal length of $-15 \; cm$. What type of mirror and lens are they?

If you want to see an enlarged image of your face, which type of mirror will you use? Where will you place your face?