17. An air bubble in a glass slab (μ = 1.5) is 5 cm deep when viewed from one face and 2 cm deep when viewed from the opposite face. The thickness of the slab is ?

17. An air bubble in a glass slab (μ = 1.5) is 5 cm deep when viewed from one face and 2 cm deep when viewed from the opposite face. The thickness of the slab is ?

(a) 7.5 cm

(b) 10.5 cm

(c) 7 cm

(d) 10 cm

Answer :  (b) 10.5 cm

\( t = x + y \)  

\( = 5\mu + 2\mu \)  

\( = 7\mu \)  

\( = 7 \times 1.5 \)  

\( = 10.5 \)