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QPages 456-457: Q1: HC Verma: Concepts of Physics - Volume 2 The Special Theory of Relativity Pages 456-457: Q1 Solution: The speed of light in glass is . Does it violate the second…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often mistake the measured speed of light in a material (e.g., $2.0\times10^8\,$m/s in glass) for the universal constant $c$, thinking any slower value breaches SR. Remember: the second postulate applies strictly to light propagating in vacuum; in a medium the reduced speed $v=c/n$ arises from photon‑matter interactions and does not contradict relativity.

The speed of light in glass is 2.0×108 m s−12.0 \times 10^8 \text{ m s}^{-1}. Does it violate the second postulate of special relativity?

Step-by-Step Verified Solution

**Answer:** No, it does not violate the second postulate of special relativity. **Step-by-Step Explanation:** The second postulate states that the speed of light in **vacuum** is the same (cc) in all inertial frames. When light travels through a medium like glass, its speed is c/μc/\mu, where μ\mu is the refractive index. This reduced speed is due to the interaction of light with the atoms of the medium, not a violation of the postulate. The postulate applies specifically to propagation in vacuum .

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