A rectangular glass block of refractive index 1.5 has an air bubble trapped inside it as shown in the diagram. When seen from the surface AB, it appears to be 4 cm deep.
(a) Calculate the actual depth of the air bubble from the surface AB.
(b) For which colour of light, blue or yellow, the apparent depth will be greater?
(c) Turning the glass block upside down, DOES NOT change the apparent depth of the air bubble. State True or False.
(a) Given,
Refractive index of glass (μ) = 1.5
Apparent depth of air bubble = 4 cm
Refractive index of glass (μ) = \frac{ \text{Real depth of air bubble}}{ \text{Apparent depth of air bubble}}
Real depth of air bubble = 1.5 × 4 = 6 cm.
So, actual depth of the air bubble from the surface AB is 6 cm.
(b) Apparent depth will increase if refractive index decreases. As wavelength increases, refractive index decreases. The wavelength of yellow light is greater than that of blue light, so the apparent depth will be greater for yellow light.
(c) When the block is turned upside down,
the real depth of the bubble is 15 − 6 = 9 cm.
Apparent depth = 9 ÷ 1.5 = 6 cm.
So, the statement is False.
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