A small pin fixed on a table top is viewed from above from a distanceof 50cm. By what distance would the pin appear to be raised if it isviewed from the same point through a 15cm thick glass slab heldparallel to the table? Refractive index of glass = 1.5. Does the answerdepend on the location of the slab?

Given distance of pin from the point where it is viewed is 50 cm, thickness of the glass slab is 15 cm and refractive index is 1.5.

Let μ be the refractive index of glass, d be the actual depth of the pin and d ′ be the apparent depth of pin, then

μ= d d ′

Substitute the values in the above expression.

1.5= 15 d ′ d ′ = 15 1.5 =10 cm

Let D be the distance at which the pin appears to be raised. Then,

D= d ′ −d

Substitute the values in the above expression.

D=15−10 =5 cm

Hence, the pin appears to be raised at distance of 5 cm.

As the angle of incidence is very small, therefore the distance would not depend upon the location of the slab.