Question

Assume that a drop of liquid evaporates by decreases in its surface energy, so that its temperature remains unchanged. What should be the minimum radius of the drop for this to be possible? The surface tension is T, density of liquid is `rho` and L is its latent heat of vaporization.
A. (a) `rhoL//T`
B. (b) `sqrt(T//rhoL)`
C. (c) `T//rhoL`
D. (d) `2T//rhoL`

Answer 1

Correct Answer - D
When radius is decrease by `DeltaR`,
`4piR^2rhoL=4piT[R^2-(R-DeltaR)^2]`
`impliesrhoR^2DeltaRL=T[R^2-R^2+2RDeltaR-DeltaR^2]`
`impliesrhoR^2DeltaRL=T2RDeltaR` [`DeltaR` is very small]
`implies R=(2T)/(rhoL)`