Whirlpool castes shadow Yesterday, while warming water in a steel bucket for taking a bath, I observed something. When I made a whirlpool with the help of my rod heater, I observed that after stabilizing, the whirlpool castes a shadow directly below it (the light bulb happened to be directly above the bucket of water). What is the possible reason behind this ?
 A: The whirlpool changes the surface of the water to make it act like a diverging lens.  Light that is incident on the whirlpool is refracted (bent) at the air/water boundary.  Since the light that would normally pass straight through the area is redirected the result is a dark area that looks like a shadow below.
A: The reason is that the surface of the water is not flat.  So, since the refractive index of the water is greater than that of air, you can think of the bucket as a lens with a very odd shape.  This lens is 'focussing' the light that passes through it, resulting in more light getting to some bits of the bottom of the bucket and less getting to others.  This is the 'shadow' which you're seeing: it's not really a shadow in the sense that no light was blocked by an opaque object, although it looks like one.
A: Consider whirlpool  like a black hole..
It has more gravity since water and some floating particles around the whirlpool are  ultimately going to get inside at some time...
As like blackhole engulfs all light  entering it..whirlpool also engulfs the light thrown on in and the shadow is casted at the bottom of bucket..
Surprisingly we can see more light at the periphery of the shadow like a solar eclipse...
