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Light travels through a glass plate of thickness t and refractive index μ. If c is the speed of light in vacuum, the time taken by light to travel this thickness of glass is

Asked in CBSE AIPMT 1996 · Snell's law, slabs and apparent depth

• (1) μ t c
• (2) (tc)/μ
• (3) 1/(μ t)
• (4) (μ t)/c

Step-by-step solution

Why the other options are wrong

• (1) comes from multiplies by c where the time divides by it; this would make the crossing take longer the faster light travels
• (2) comes from divides a length by a refractive index and multiplies by a speed, which leaves m² s⁻¹ rather than a time
• (3) comes from is a reciprocal length with no speed in it at all, so it cannot be a time

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