In figure, pressure inside a spherical drop is more than pressure… - Vidyadip

MCQ

In figure, pressure inside a spherical drop is more than pressure outside. (S = surface tension and r = radius of bubble)

The extra surface energy if radius of bubble is in creased by $\Delta r$ is

A
$2 \pi r \Delta r S$
B
$4 \pi r \Delta r S$
C
$10 \pi r \Delta r S$
D
$8 \pi r \Delta r S$

✓

Answer

(d) $8 \pi r \Delta r S$
Explanation: Suppose a spherical drop of radius $r$ is in equilibrium. If its radius increases by $\Delta r$. The extra surface energy is $\left|4 \pi(r+\Delta r)^2-4 \pi r^2\right| S=8 \pi r \Delta r S$

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