# An air bubble in a glass slab with refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness (in cm) of the slab is Option 1) 8 Option 2) 10 Option 3) 12 Option 4) 16

P Prateek Shrivastava

As we learnt in

Relation between real depth and apparent depth -

$\frac{n_{i}}{d}= \frac{n_{r}}{d{}'}$

- wherein

$n_{i}$ = Refractive index of medium of incident.

$n_{r}$ = Refractive index of medium of refraction.

d = distance of object.

$d{}'$ = apparent  depth

Apparent depth=5cm  from one side

$\therefore$ Real depth=1.5x5=7.5 cm

apparent depth=3cm from other side

$\therefore$ Real depth from other side =3x1.5cm=4.5

$\therefore$ Thickness of slab=7.5cm+4.5cm=12cm

Option 1)

8

This option is incorrect

Option 2)

10

This option is incorrect

Option 3)

12

This option is correct

Option 4)

16

This option is incorrect

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