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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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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.

Numerical
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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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Chapter 4: Refraction of Light at Plane Surfaces - EXERCISE - 4 (C) [Page 92]

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Selina Physics [English] Class 10 ICSE
Chapter 4 Refraction of Light at Plane Surfaces
EXERCISE - 4 (C) | Q 3. | Page 92

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