A fish is vertically below a flying bird moving vertically down toward water surface. The bird will appear to the fish to be

μ1−u+μ2v=μ2−μ1R For a plane surface, R=∞∴ μ1−u+μ2v=0or μ2v=μ1u or μv=1uor v=μ2uClearly, to the fish, the bird appears farther than its actual distance. Again, dvdt=μdudtor Apparent speed of bird = Refractive index x Actual speed of bird.