An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is

1. 10

2. 12

3. 16

4. 8

Doubtly Asked 30 Oct 2026 NEET UG 2016 Phase 2 Practice test neet Save WhatsApp Report

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Answer: 2. 12

Apparent depth $=\dfrac{\text{real depth}}{\mu}$. The bubble is at a fixed real depth $x$ from one face and $t-x$ from the other.

$\dfrac{x}{1.5}=5\Rightarrow x=7.5$ cm; $\dfrac{t-x}{1.5}=3\Rightarrow t-x=4.5$ cm.

$$t=7.5+4.5=12\ \text{cm}$$

Equivalently, $t=\mu(5+3)=12$ cm. Option (2).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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