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In a worked example, the table gives water's index of refraction as 1.333. Using n equals c over v with c equals 3.00 x 10^8 m/s, what is the speed of light in water?
A3.00 x 10^8 m/s
B1.33 x 10^8 m/s
C4.00 x 10^8 m/s
D2.25 x 10^8 m/s
Answer & Solution
Correct answer: D. 2.25 x 10^8 m/s
1. Rearranging n = c/v gives v = c/n.
2. Substituting values: v = (3.00 x 10^8 m/s) / 1.333.
3. Carrying out the division gives v = 2.25 x 10^8 m/s.
4. 1.33 x 10^8 m/s wrongly treats the index itself as if it were a fraction of c to multiply by.
5. 3.00 x 10^8 m/s repeats the vacuum speed without applying the index at all.
_Source: OpenStax Physics (CC BY 4.0), Ch 16 "Mirrors and Lenses", section 16.2 Refraction_
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