Question $4$

$5$ pts

What is the smallest angle $($in degrees$)$ with respect to the normal that light should be incident onto a water$-$aif interface from the water side so that it does not escape into air $($assume the refractive index of water is $1\mathrm{.}33)?$

$20$

$50\mathrm{.}2$

$48\mathrm{.}8$

$70\mathrm{.}5$