Light takes 8.9 ns to cover 20 m in water
Explanation:
The index of refraction of a medium is equal to the ratio between the speed of light in a vacuum and the speed of light in the medium:
[tex]n=\frac{c}{v}[/tex]
where
[tex]c=3\cdot 10^8 m/s[/tex] is the speed of light in a vacuum
v is the speed of light in the medium
For water,
[tex]n=1.33[/tex]
So the speed of light in water is
[tex]v=\frac{c}{n}=\frac{3\cdot 10^8}{1.33}=2.25\cdot 10^8 m/s[/tex]
Therefore, the distance covered by light in water in a time interval t is
[tex]d=vt[/tex]
Here we want to know the time taken for light to cover a distance of
d = 20 m
Solving the equation for t, we find
[tex]t=\frac{d}{v}=\frac{20}{2.25\cdot 10^8}=8.9\cdot 10^{-8} s = 89 ns[/tex]
Learn more about refraction here:
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