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The refractive index of glass is 1.6 then the speed of light in glass will be ________ speed of light in vacuum is 3.0 × 10⁸ ms⁻¹.

Asked in GUJCET 2024 · Snell's law, slabs and apparent depth

• (1) 1.66 × 10⁸ ms⁻¹
• (2) 1.88 × 10⁸ ms⁻¹
• (3) 1.22 × 10⁸ ms⁻¹
• (4) 1.48 × 10⁸ ms⁻¹

Step-by-step solution

Why the other options are wrong

• (1) 1.66×10⁸ ms⁻¹ is c/(1.8) — it needs an index of 1.8. With n=1.6 the quotient is 1.875, not 1.66.
• (3) No single slip produces 1.22×10⁸ ms⁻¹. Sanity check: v=c/n with n=1.6 lies between c/2=1.5×10⁸ and c, so any answer below 1.5×10⁸ ms⁻¹ is too slow.
• (4) 1.48×10⁸ ms⁻¹ is close to half the vacuum speed, which would need n≈2.0. An index of 1.6 slows light by a factor of 1.6, not 2.

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