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

The apparent depth of the bubble as seen from one surface = d₁' = 5 cm
Therefore, the real depth of the bubble from one surface d₁ = μd₁' = 1.5 × 5 cm = 7.5 cm
Similarly, the real depth of the bubble from the other surface = d₂ = μd₂' = 1.5 × 3 cm = 4.5 cm
Hence, the thickness of the glass is d₁ + d₂ = 7.5 cm + 4.5 cm = 12 cm