A glass slab of 16 cm thickness has its bottom surface silvered. An air bubble is located inside the glass slab at a distance of 8 cm from the top surface. The refractive index of glass is 1.6. Which of the following correctly represents the number of images seen by an observer looking vertically downwards from air onto the top surface?

Step-by-step solution

The observer will see two primary images of the air bubble. The first image is formed by the direct refraction of light from the bubble through the top surface of the glass slab. Real depth of the bubble from the top surface, x₁ = 8 cm. Apparent depth of the first image, d₁ = x₁ = 8 1.6 = 5 cm. The second image is formed by the light that travels downwards, reflects from the silvered bottom surface, and then refracts out through the top surface. Distance of the bubble from the bottom silvered surface = 16 - 8 = 8 c