Prove that
Refractive index = real depthapparent depth
This can be proved by the following picture:
The refractive index of the medium a with respect to medium b is given by,
bμa=sin isin r⇒aμb=sin rsin i
In △OAB,sin i=ABOBIn △O′AB,sin r=ABO′B
aμb=ABO′BABOB=ABO′B×OBAB=OBO′B
As the points, A and B are very close, OB≈OA (real depth) and O′B≈O′A (apparent depth).
aμb=real depthapparent depth
Hence proved