A ray light is incident at the glass-water interface at an angle i, it merges finally parallel to the surface of water, then the value of μg would be
1 /sin i
At first surface;
sinisinr=μωμg=43μg ....(1)
A second surface;
sinr=1μω=34 ....(2)
putting this value in (1)
4sini3=43μg
⇒μg=1sini