A concave mirror has radius of curvature of 40 c m . It is at the bottom of a glass that has water filled up to 5 c m (see figure). If a small particle is floating on the surface of water, its image as seen, from directly above the glass, is at a distance d from the surface of water. The value of d is close to: (Refractive index of water = 1.33 )

Question

A concave mirror has radius of curvature of 40 c m . It is at the bottom of a glass that has water filled up to 5 c m (see figure). If a small particle is floating on the surface of water, its image as seen, from directly above the glass, is at a distance d from the surface of water. The value of d is close to: (Refractive index of water = 1.33 ), 13.4 c m, 8.8 c m, 6.7 c m, 11.7 c m

MARKS App · Accepted Answer

Given u = - 5 c m f = - R 2 = - 40 2 = - 20 c m Now 1 v + 1 u = 1 f 1 v = 1 - 20 = 1 - 5 ∴ v = + 20 3 c m Then Object distance d = 5 + 20 3 = 35 3 c m (below water surface) The image after refraction d ' = d μ 2 μ 1 = 35 3 1 1.33 = 8.77 d ' ≃ 8.8 c m

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