A pile 4 m high stands in the lake,such that it protrudes y 1m above the surface of water.Determine th elength of the shadow of the pile on the botton of lake,when the sunrays make an angle of `45^@` with the water surface.Tke refractive index of water,`mu=4//3`.
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A convex lens of refractive index 1.5 has a focal length of 18 cm in air.Calculate the change in focal length,when it is immersed in water of refractive index 4//3 .

In a double-slit experiment the angular width of a fringe is found to be 0.2^@ on a screen placed 1 m away. The wavelength of light used is 600 nm. What will be the angular width of the fringe if the entire apparatus is immersed in water? Take refractive indexof water to be 4/3 .

Nazima is fly fishing in a stream. The tip of her fishing rod is 1.8 m above the surface of the water and the fly at the end of the string rests on the water 3.6 m away and 2.4 m from a point directly under the tip of the rod. Assuming that her string (from the tip of her rod to the fly) is taut, how much string does she have out ? If she pulls in the string at the rate of 5 cm per second, what will the horizontal distance of the fly from her after 12 seconds ? .

The refractive index of water is 4//3 .How much time will light take to travel through a water column of length 500 m?

Refractive index of water is 5//3 . A light source is placed in water at a depth of 4m. Then what must be the minimum radius of disc placed on water surface so that the light of source can be stopped?

A fish looking up through the water sees the outside world contained in a circular horizon.If the refractive index of water is 4//3 and fish is 12 cm below the surface of water,then the radius of the circular horizon is