Question

Soap bubbles can be formed floating in air by blowing soap solution in air, with the help of a glass tube, but not water bubbles. It is because
A. The excess pressure inside the water bubble is more due to large surface tension.
B. The excess pressure inside the water bubble is less due to large surface tension.
C. The excess pressure inside the water bubble is more due to large viscosity.
D. The excess pressure inside the water bubble is less due to less viscosity.

Answer 1

The difference in pressure between in and around of a bubble depends on the surface tension and the bubble’s radius. Surface tension means liquid surfaces tend to reduce to the lowest surface area.

Complete step by step answer:
Cohesive forces are considered attractive forces between molecules of the same type. In surface tension cohesive forces between the molecules allow a substance to compact to the smallest surface area possible. Cohesive forces drag molecules on the surface inward, thereby reducing the surface area. Molecules feel zero net force within the liquid because they have neighbours on both sides.
The surface of a liquid acts as if a stretching membrane is surrounding it. Membrane capacity depends on the liquid. The strength of this membrane is much higher for soapy water than normal water.
All liquid structure minimises the surface area if there are no opposing external forces present. Since, the sphere is the object with the lowest surface to volume ratio, soap bubbles and rain drops are spherical.
In a soap bubble because of the pressure difference between the inside and the outside layer, the surface friction balances the external force.
So, from the above discussion we can see how surface tension works inside a bubble.
Hence, soap bubbles can be formed floating in air by blowing soap solution in air, with the help of a glass tube, but not water bubbles due to the excess pressure inside the water bubble being more due to large surface tension.

So, the correct answer is “Option A”.

Note:
Surface tension is the secret to creating bubbles. If detergent or soap is applied to water, the surface tension is lowered so that bubbles can form.