Excess Pressure Inside a Liquid Drop (ΔP = Pi − Po = 2S/r)
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ΔP = Pi − Po = 2S/r
What each symbol means
| Symbol | What it stands for |
|---|---|
| S | Surface tension of the liquid (N/m) |
| r | Radius of the drop (m) |
| Pi | Pressure inside the drop (Pa) |
| Po | Pressure outside the drop (Pa) |
| ΔP | Excess pressure inside the drop over outside (Pa) |
When to use this
For a liquid drop or air cavity in a liquid (one surface). Derived by balancing surface energy increase (8πr Δr S) against work done by pressure difference (ΔP × 4πr² Δr). Smaller drops have higher internal pressure. Concave side always has higher pressure.