What Angle Must Light Make at the Water-Oil Interface to Prevent Escape?

[rbnphlp]

A tank of water (nwater = 1.33) is co v e r e d w i t h a l a y e r o f oi l (noil = 1.48),
a b o v e w h i c h is a i r ( n ~ r - - 1.00). W h a t a n g l e m u s t a b e a m o f l i g h t , o r i g i n a t i n g i n t h e t a n k , m a k e a t t h e w a t e r - o i l
i n t e r f a c e i f n o l i g h t is t o e s c a p e ?

my calculations ..

n_air sin \theta_i=n_oil sin\theta _t

n_oil sin \theta_t=n_water sin\theta_r

and total internal reflection occurs when angle is larger than the critical angle ,but doesn't work out ..any help?

 

[chrisbaird]

Please reformat your question so it is intelligible. I am assuming you are neglecting thin-film interference.