Question:

A mercury drop of radius $1 \,cm$ is sprayed into $10^{6}$ drops of equal size. The energy expended in joule is (surface tension of mercury is $460 \times 10^{-3}\,N / m$ ):

Updated On: Jun 23, 2023
  • $0.057$
  • $5.7$
  • $5.7 \times 10^{-4}$
  • $5.7 \times 10^{-6}$
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The Correct Option is A

Solution and Explanation

$R =1 \,cm , n =10^{6}$ $\Delta \bigcup=4 \pi R ^{2}\left( n ^{1 / 3}-1\right) T$ $=4 \pi \times 10^{-4}\left(10^{2}-1\right) 460 \times 10^{-3}$ $=0.057\, J$
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Concepts Used:

Surface Tension

The amount of energy required to increase the liquid's surface area by one unit area is known as surface tension. In other words, it is a property of the liquid surface to resist force.

Surface tension is defined as,

The ratio of the surface force F to the length L along which the force acts.

Mathematically, the surface tension formula can be expressed as follows:

T=F/L

Where,

  • F is the force per unit length
  • L is the length in which force act
  • T is the surface tension of the liquid

Read More: Detergents and Surface Tension

Factors affecting surface tension:

  • Impurities: The surface tension decreases with the addition of impurities.
  • Surfactants: Adding surfactants in liquids lowers the tension of water making it interrupt aside or get susceptible.
  • Temperature: The surface tension of a liquid reduces as the temperature rises.

The Unit of Surface Tension:

The SI unit of Surface Tension is Newton per Meter or N/m.