Properties of Matter 4 Question 16

18. As the bubble moves upwards, besides the buoyancy force the following forces are acting on it.

(2008,4 M)

(a) Only the force of gravity

(b) The force due to gravity and the force due to the pressure of the liquid

(c) The force due to gravity, the force due to the pressure of the liquid and the force due to viscosity of the liquid

(d) The force due to gravity and the force due to viscosity of the liquid

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Answer:

Correct Answer: 18. dQdtr5

Solution:

  1. Surface Tension force =2πb×2Tsinθ

Mass of the air per second entering the bubble =ρAv

Momentum of air per

= Force due to air =ρAv2

The bubble will separate from the tube when force due to moving air becomes equal to the surface tension force inside the bubble.

2πb×2Tsinθ=ρAv2

putting sinθ=br,A=πb2 and solving, we get

r=4Tρv2



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