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Question:

Assume that a drop of liquid evaporates by decrease in its surface energy, so that its temperature remains unchanged. What should be the minimum radius of the drop for this to be possible?

T/ρL

ρL/T

√T/ρL

2T/ρL

Solution:

ρ4πR²ΔRL = T4π[R² − (R−ΔR)²]
ρR²ΔRL = T[R² − R² + 2RΔR − ΔR²]
ρR²ΔRL = T2RΔR (ΔR is very small)
R = 2T/ρL