Light passing through water, air and diamond all travel slower than light in a vacuum. Ranked from fastest to slowest, which order is correct?
AAir, then water, then diamond
BDiamond, then water, then air
CWater, then diamond, then air
DDiamond, then air, then water
Answer & Solution
Correct answer: A. Air, then water, then diamond
1. Air slows light only slightly, to 99.97 percent of c, so air is close to vacuum speed.
2. Water slows light more, to three-fourths of c, which is 75 percent of c.
3. Diamond slows light down to just 41 percent of c, the slowest of the three.
4. Ranking from fastest to slowest therefore gives air first, water second, and diamond last.
5. Any ordering that puts diamond ahead of water or air ignores that 41 percent is the smallest of the three fractions.
_Source: OpenStax Physics (CC BY 4.0), Ch 15 "Light", section 15.2 The Behavior of Electromagnetic Radiation_
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