The image shows the path of light as it travels from one medium to another.
$9$. Based on the refraction observed, which pair of media could represent Medium $1$ and Medium $2$?

	Medium $1$	Medium $2$
$A$.	Water	Kerosene
$B$.	Kerosene	Diamond
$C$.	Flint glass	Water
$D$.	Kerosene	Flint glass

$10$. The power of a lens $(P)$ is calculated by the formula, $P = \frac{1}{f}$, where $f$ is the focal length of the lens in meters. A lens has a focal length of $-0.25 \ m$. Is it a convex lens or a concave lens? Explain your answer.

(N/A) $9$. $C$. In the image, the light ray bends away from the normal as it enters Medium $2$. This indicates that light is traveling from a denser medium to a rarer medium (refractive index of Medium $1$ > refractive index of Medium $2$). Among the options, the refractive index of flint glass $(n \approx 1.66)$ is greater than that of water $(n \approx 1.33)$.
$10$. Given: Focal length $(f)$ = $-0.25 \ m$.
Using the formula $P = \frac{1}{f}$, $P = \frac{1}{-0.25} = -4 \ D$.
A lens with a negative focal length is a concave lens. Concave lenses are diverging lenses and by sign convention, their focal length is always taken as negative.