[填空题]
What is the critical anglen3r)ft8 jp4qk for the interface between water wks6bu h(c+ts/.b7c sxh+t2hand Lucite? To be totally internally reflected, the light muhucbc.+ 6b shtkw +/(7sxhst2st start in which material?
$\theta$ = $^{\circ}\,$
{water|Lucite|}
