Class 12 Physics
CBSE and UP Board
Ray Optics and Optical Instruments
Chapter-9 Exercise 9.16
NCERT Solutions for Class 12 Physics Chapter 9 Question-16
A small pin fixed on a table top is viewed from above from a distance of 50 cm. By what distance would the pin appear to be raised if it is viewed from the same point through a 15 cm thick glass slab held parallel to the table? Refractive index of glass = 1.5. Does the answer depend on the location of the slab?
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Actual depth of the pin, d = 15 cm
Apparent depth of the pin = d’
Refractive index of glass,μ = 1.5
Ratio of actual depth to the apparent depth is equal to the refractive index of glass, i.e.
μ = d/d’
Therefore ,d’ = d/μ
= 15/1.5 = 10 cm
The distance at which the pin appears to be raised = d’ – d = 15 – 10 = 5 cm
For a small angle of incidence, this distance does not depend upon the location of the slab.