Answer:
The light slows down to a speed equal to 3/4 of its original value
Explanation:
The speed of light in a medium is given by:
[tex]v=\frac{c}{n}[/tex]
where
[tex]c=3.0\cdot 10^8 m/s[/tex] is the speed of light in a vacuum
n is the index of refraction of the medium
For light entering air, we have that the light enters a medium with index of refraction of
[tex]n=\frac{4}{3}[/tex]
Therefore, its speed changes as follows
[tex]v=\frac{c}{\frac{4}{3}}=\frac{3}{4}c=\frac{3}{4}(3\cdot 10^8 m/s)=2.25\cdot 10^8 m/s[/tex]
