Fresh water has an index of refraction of 1.333. Taking the vacuum speed of light as 3.00 x 10^8 m/s, what is the speed of light in fresh water?

1. The speed of light through matter is less than in a vacuum because light interacts with the atoms of the material. 2. Rearranging n = c divided by v gives v = c divided by n. 3. Substituting with units, v = (3.00 x 10^8 m/s) divided by 1.333 = 2.25 x 10^8 m/s. 4. The answer is smaller than the vacuum value, as it must be for any material. 5. The 4.00 x 10^8 m/s option comes from multiplying by n, which would put light above its vacuum speed. _Source: OpenStax College Physics (CC BY 4.0), Ch 25 "Geometric Optics", section 25.3 The Law of Refraction_