The Index of Refraction refers to:

Question

BlackTom AI · Accepted Answer

Index of refraction quantifies how fast light travels in a material compared to in air (or vacuum). It is defined by n = c / v, where c is the speed of light in vacuum (≈3.00 × 10^8 m/s) and v is the speed of light in the material.

1. Relevant knowledge points and concepts
- Refractive index (n) = c / v. A larger n means light travels more slowly in that medium.
- In optics, comparisons are usually to vacuum (nvac = 1). For practical gemology, air (n ≈ 1.0003) is effectively 1, so saying “compared to the air around it” is acceptable.
- Snell’s law (n1 sinθ1 = n2 sinθ2) uses refractive indices to predict bending (refraction) at boundaries; the index itself is a ratio of speeds.

2. Step-by-step reasoning
- The statement “the velocity of light through a gem compared to the air around it” corresponds directly to the ratio v_air / v_gem, which is the inverse of v_gem / v_air but commonly expressed as n_gem = c / v_gem. Because air’s index ≈1, this effectively compares the gem’s light speed to that in air/vacuum.

3. Intermediate calculation example
- Suppose a gem has n = 1.6. Then v_gem = c / n = (3.00 × 10^8 m/s) / 1.6.
- Compute: 3.00 × 10^8 ÷ 1.6 = 1.875 × 10^8 m/s.
- So light in that gem travels ≈1.875 × 10^8 m/s, slower than in air/vacuum.

4. Why the correct answer is correct
- The refractive index is literally defined by the ratio of light speeds; hence saying it “refers to the velocity of light through a gem compared to the air around it” is a correct, practical description.

5. Why other possible interpretations are incorrect
- It is not the material’s density, color, or directly the angle of bending (though the index determines the bending via Snell’s law). Saying it equals angle or density confuses cause and effect.

6. Conclusion
- Therefore the provided answer — “the velocity of light through a gem compared to the air around it” — correctly describes the index of refraction. This matches the authoritative answer.

The Index of Refraction refers to:单项选择题

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