The radii of two soap bubbles are R₁ and R₂ respectively. The ratio of masses of air in them will be
Correct Answer :
(P+4T/R₁)R₁³/(P+4T/R₂)R₂³
Solution :
To find the ratio of the masses of air inside two soap bubbles of radii and , we can use the ideal gas equation and the concept of excess pressure inside a soap bubble.
According to the ideal gas equation:
where:
- is the absolute pressure of the air inside the bubble,
- is the volume of the bubble,
- is the number of moles of air, which is proportional to the mass (, where is the molar mass of air),
- is the universal gas constant, and
- is the absolute temperature.
Since the temperature and the molar mass of air are the same for both bubbles, the mass of air inside a bubble is directly proportional to the product of its absolute pressure and volume:
For a soap bubble of radius , surface tension , and atmospheric pressure outside:
The excess pressure inside the soap bubble is given by:
Thus, the absolute pressure inside the bubble is:
The volume of a spherical bubble of radius is:
Substituting the absolute pressure and volume into the relation for mass, we get:
Since is a constant, we have:
Therefore, the ratio of the masses of air in the two bubbles is:
This matches the correct option.
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