JEE Main Physics Class 11 Physical world and Measurements Part 1 Questions

Given, the radius of the spherical drop
r=(‌

3

40π

)1/3×10−3cm
The volume of 100 spherical drops, V=100×‌

4πr3

3

Substituting the value of the radius in the above equation, we get
V=100×‌

4π

3

×‌

3

40π

×10−9
V=10−8cm3
Now, Volume of the film = Area of the film × Thickness of the film
⇒ Volume of the film =4×t
The film is made up of 100 spherical drops.
∴ The volume of the film = Volume of 100 spherical drops
4t=10−8⇒t=25×10−12m
The thickness of the oleic layer,
t0=0.01×t=25×10−14m
Comparing with x×10−14, we get x=25