The radius of Snell’s window can be deduced with the illustration as shown in figure. Light is seen from a point A at a depth d. The Snell’s law in product form, equation n2sin i = n2sin r for the refraction happening at the point B on the boundary between the two media is
n sin i = n sin 90° ……. (1)
n sin i = n ∵ sin 90° = 1
sin i = …….. (2)
From the right angle triangle ∆ABC,
Equating the above two equation (3) and equation (2).
If the rarer medium outside is air, then, n2 = 1, and we can take n1 = n
