The **excess pressure** inside a spherical liquid drop of radius $r$ and surface tension $T$ is:
A$T/r$
B$2T/r$
C$4T/r$
D$8T/r$
Answer & Solution
Correct answer: B. $2T/r$
For a single-surface liquid drop, excess pressure = $2T/r$. For a soap bubble (two surfaces — inside and outside), it's $4T/r$. Smaller drops have larger internal pressure — that's why tiny droplets evaporate faster.
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