Q71
General SciencePhysics
A drop of water is broken into two drops. The sum of which property of the two drops is equal to that of the single one?
- a.Radius
- b.Surface area
- c.Surface energy
- d.Volume
Answer: (D) Volume
Mass, and therefore volume for a liquid of fixed density, is conserved when a drop is divided: $R^3=r_1^3+r_2^3$. Radii do not add up in this way. The total surface area of the two smaller drops is greater than that of the original drop, so the total surface energy (surface tension × area) is also greater; that is why work has to be done to break a drop. This is the reverse of the case where two drops merge and energy is released.