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Question
A postage stamp kept below a rectangular glass block of refractive index 1.5 when viewed from vertically above it, appears to be raised by 7.0 mm. Calculate the thickness of the glass slab.
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Solution
Refractive index of glass = 1.5
Let the thickness of slab = x mm
stamp raised by = 7 mm
∴ observed depth. = (x - 7) mm
R.I = `"Real depth"/"observed depth"`
= `3/2 = x/((x - 7))`
∴ 3x - 21 = 2x
Or x = 21 mm = 2.1 cm
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