Example of Ray optics | Learn Physics

Example of Ray optics

Example  of Ray optics: a small fish, 0.4 m below the surface of a lake, is viewed through a simple converging lense of focal length 3 m. the lense is kept at 0.2 m above the water surface, such that the fish lies on the optical axis of the lens. Find the image of the fish seen by the observer. The refractive index of water is 4/3.

Solution:

Here, the first refraction takes place from water to air at plane water air interface.

Now                  u = -0.4m,    v=?

As                     ^wµ_a  = 1/ ^aµ_w =v/u

                          1/(4/3) =u/-0.4             v = 0.3m

This image acts as an object for the lens.

Now,                     v₁=?    U₁=    - (0.3 + 0.2)=-0.5 m

                                 F = +3m

As                       (1/v₁) – (1/u₁) =  1/f

                              1/v₁ =( 1/f)+ (1/u₁) = (1/3)-(1/0.5)=-5/3

                              V₁ = -(0.4 + 0.2)m

Hence final image of the fish is at -0.4 m. it concides with the actual position of the fish.