Question

An infinitely long cylindrical water filament of radius r is surrounded by air. Assume water and air to be static. The pressure outside the filament is $P_{out}$ and the pressure inside is $P_{in}.$ If $γ$ is the surface tension of the water-air interface, then $P_{in} − P_{out}$ is

• A. $2γ/r$
• B. 0
• C. $γ/r$
• D. $4γ/r$

Official answer: $γ/r$