Rahul sees a flock of birds. He watches as the flying birds land in neat little rows on several power lines. Which change of sta
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The intensity is defined as the ratio between the power emitted by the source and the area through which the power is calculated:
(1)
where
P is the power
A is the area
In our problem, the intensity is
. At a distance of r=6.0 m from the source, the area intercepted by the radiation (which propagates in all directions) is equal to the area of a sphere of radius r, so:
And so if we re-arrange (1) we find the power emitted by the source:
where
P is the power
A is the area
In our problem, the intensity is
And so if we re-arrange (1) we find the power emitted by the source:
When light travels from a medium with greater refractive index 
to a medium with smaller refractive index 
, there exists an angle (called critical angle) above which the light is totally reflected, and the value of this angle is given by
In this problem, we know that the critical angle is
, so we can find the ratio between the refractive indices of the two mediums:
and since the second medium is air (n=1.00), the refractive index of the first medium is
In the second part of the problem, we have light entering from air (
) at angle of incidence of 
, into the second medium with 
. By using Snell's law, we can find the angle of refraction of the light inside the medium:
In this problem, we know that the critical angle is
and since the second medium is air (n=1.00), the refractive index of the first medium is
In the second part of the problem, we have light entering from air (