CBSE Class 10 Answered

Yes, it's true that maximum lateral displacement possible is equal to the slab thickness, the light ray don't exactly travels along the normal in the medium, the glass slab.

Let's analyse, consider the topmost interface - air to glass slab.

sin i/ sin r = μ

sin 90/sin r = μ

sin r = 1/μ

Since sin r = 1/μ = 1/1.5 = 2/3             ................for glass

The angle of refraction in the glass slab in not ZERO, as drawn in the diagram, but it's finite and nonzero.

Now this angle of refraction r, becomes the angle of incidence for glass to air travel.

sin i'/ sin r' = 1/μ                           .........since the ray now travels from glass to air.

but sin i' = sin r = 1/μ

Hence sin r' = 1 and r' = 90.

This shows that the ray from glass to air is refracted at an angle to 90 to the normal, which means it's travelling along the glass air interface.

Regards,

Team,

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