If the refractive index of water is 1.33, what does this mean about the speed of light in water compared to its speed in vacuum?
Correct: B
The refractive index (n) of a medium is defined as the ratio of the speed of light in vacuum (c) to the speed of light in that medium (v): n = c/v. Therefore, v = c/n. If n = 1.33, then v = c/1.33. This means the speed of light in water is c/1.33, which is 1.33 times slower than its speed in vacuum.