A vesserl contains a slab of glass 8cm thick and of refractive index 1.6 . Over the slab, the vessel is filled by oil of refractive index `mu` upto height 4.5 cm and then by another liquid, i.e., water of refractive index `4//3` and height 6cm as shown in Figure. An observer looking down from above observer that a mark at the bottom of glass slab appears to be raised up to a position 6cm from bottom of the slab. Find refractive index of oil `(mu)` .

Explanation

Point 'O' is at the bottom and boundaries of the medium are parallel.
So, total apparent shift (OI)=shift due to glass+shift due to oil+shift due to water is
`8(1-(1)/(1.6)
)+4.5(1-(1)/(mu))+6(1-(1)/(4//3))=6`
After solving, we get `mu=1.5`