00:02
Hello and welcome to this video solution of numerate.
00:05
Here it's given that a point source is submerged 2 .2 meters below the surface of a lake.
00:10
So let me draw.
00:12
So this is the source and this is at a height of 2 .2 meters.
00:19
And of the lake and emits ray in all direction.
00:25
Now on the surface of the lake directly above the source the area illuminated is in a form of a circle.
00:32
Now you have to calculate the radius of the circle.
00:34
So this is pretty simple.
00:36
So let's say this is the normal you have got on the surface or the other in the interface rather of this water and air.
00:46
Now the other ray will pass from the source and it will do a grazing incidence.
00:53
Sort of like this.
00:56
Now for that what you need is this angle theta.
01:02
And this theta is a critical angle between this water and air.
01:10
So the critical angle formula is sin ic is equal to 1 by mu...