i = 50°
r' = 50°-20° = 30°
n[tex]_{aer}[/tex]=1
Formula lui Snell
[tex]n_{aer}\cdot sin(\angle i)=n_{lichid}\cdot sin(\angle r) \\ \\ 1\cdot sin50=n_{lichid}\cdot sin30 \\ \\ n_{lichid}\cdot0,5=sin50 \\ \\ n_{lichid}=2\cdot sin50\approx2\cdot0,77 \\ \\ n_{lichid}\approx1,54[/tex]