Ray Optics and Optical Instruments - Result Question 16
16. An air bubble in a glass slab $(\mu=1.5)$ 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) $10 cm$
[2000]
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Answer:
Correct Answer: 16. (b)
Solution:
(b) $1.5=\frac{\text{ Real depth }(R_1)}{\text{ Apparent depth }(5 cm)}$
$\therefore R_1=1.5 \times 5=7.5 cm$
For opposite face,
$1.5=\frac{R_2}{2} \Rightarrow R_2=3.0 cm$
$\therefore$ Thickness of the slab $=R_1+R_2$
$ =7.5+3=10.5 cm $
If object and observer are situated in different medium then due to refraction, object appears to be displaced
Refractive index, $\mu=\frac{\text{ Real depth }(h)}{Apparent depth(h^{\prime})}$
Real depth > Apparent depth
In case object is in rarer medium and object is in denser medium then, $\mu=\frac{h^{\prime}}{h}$
Real depth < apparent depth
