# NCERT Class 11 Physics Solutions: Chapter 10 – Mechanical Properties of Fluids-Part 9 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 10.20:

What is the excess pressure inside a bubble of soap solution of radius , given that the surface tension of soap solution at the temperature ? If an air bubble of the same dimension were formed at depth of inside a container containing the soap solution (of relative density what would be the pressure inside the bubble? ( atmospheric pressure is 1

Excess pressure inside the soap bubble is

Pressure inside the air bubble is

Surface tension of the soap solution,

Relative density of the soap solution

Density of the soap solution,

Air bubble formed at a depth,

Atmospheric pressure

Acceleration due to gravity,

Hence, the excess pressure inside the soap bubble is given by the relation:

Therefore, the excess pressure inside the soap bubble is

The excess pressure inside the air bubble is given by the relation:

Therefore, the excess pressure inside the air bubble is

At a depth of the total pressure inside the air bubble

Therefore, the pressure inside the air bubble is

Question 10.21:

A tank with a square base of area is divided by a vertical partition in the middle. The bottom of the partition has a small-hinged door of area . The tank is filled with water in one compartment, and an acid (of relative density ) in the other, both to a height of compute the force necessary to keep the door close.

Base area of the given tank,

Area of the hinged door,

Density of water,

Density of acid,

Height of the water column,

Height of the acid column,

Acceleration due to gravity,

Pressure due to water is given as:

Pressure due to acid is given as:

Pressure difference between the water and acid columns:

Hence, the force exerted on the door

Therefore, the force necessary to keep the door closed is

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