Liquid Drop Shape and Pressure – Rankers Physics

Surface Tension and Viscosity: Practice Problem & Solution

Assertion (A): The shape of a liquid drop is spherical. Reason (R): The pressure inside the drop is greater than that of outside.  
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Surface Tension and Viscosity. Understanding the underlying formula is key to arriving at the correct answer below:

Concept: Surface tension and pressure difference. Assertion (A) is true because surface tension tends to minimize the surface area of a liquid for a given volume, and a sphere has the minimum surface area. Reason (R) is true; due to surface tension, there is an excess pressure inside a spherical liquid drop, given by \(P_{in} - P_{out} = \frac{2T}{R}\). This excess pressure balances the inward pull of surface tension, thus R correctly explains A.

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