A liquid drop and a soap bubble have the same radius R and the same surface tension S. If their excess internal pressures are ΔP(drop) and ΔP(bubble), respectively, what is the ratio ΔP(drop) : ΔP(bubble)?
Options

Question

A liquid drop and a soap bubble have the same radius R and the same surface tension S. If their excess internal pressures are ΔP(drop) and ΔP(bubble), respectively, what is the ratio ΔP(drop) : ΔP(bubble)?

Options

G1 Physics · Accepted Answer

A liquid drop has one liquid-gas interface. Therefore, ΔP(drop) = 2S/R. A soap bubble has two liquid-gas surfaces. Therefore, ΔP(bubble) = 4S/R. Hence, ΔP(drop) : ΔP(bubble) = 2S/R : 4S/R = 1 : 2. Correct option: B.