Refraction of Light

Question

A postage stamp kept below a rectangular glass slab of refractive index 1.5 when viewed from vertocally above it,appears to be raised by 7.0 mm.Calculate the thickness of the glass slab.

Answer 1

Refractive index = Real depth / Apparent  depth     ( When viewed vertically)

 

1.5 = Thickness of slab / Apparent depth

       = Thickness of slab / (Thickness - raise)

       = Thickness / (Thickness - 7 .0 )

Gives Thickness = 21.0 mm