$A$ beam of monochromatic blue light of wavelength $4200 \, \mathring{A}$ in air travels into water $(\mu = 4/3)$. Its wavelength in water will be.......$\mathring{A}$

$A$ girl standing at point $P$ on a beach wishes to reach a point $Q$ in the sea as quickly as possible. She can run at $6 \, kmh^{-1}$ on the beach and swim at $4 \, kmh^{-1}$ in the sea. She should take the path

State Snell's law of refraction.

$A$ beam of light propagating in medium $A$ with index of refraction $n(A)$ passes across an interface into medium $B$ with index of refraction $n(B)$. The angle of incidence is greater than the angle of refraction; $v(A)$ and $v(B)$ denote the speed of light in $A$ and $B$. Then which of the following is true?

The refractive index of a material for infrared light is:

The incorrect statement about the refractive index for a pair of media is: