A soap bubble is being blown at the end of a very narrow tube of radius b. Air (density ρ) moves with a velocity ‘v’ inside the tube and comes to rest inside the bubble. The surface tension of the soap solution is T. After some time the bubble, having grown to a radius ‘r’, separates from the tube. Find the value of ‘r’. Assume that r>>b so that you can consider the air to be falling normally on the bubble’s surface.
 

• A

  $\frac{4\mathrm{T}}{{\mathrm{\rho v}}^3}$

• B

  $\frac{4\mathrm{T}}{\mathrm{\rho v}}$

• C

  $\frac{2\mathrm{T}}{{\mathrm{\rho v}}^2}$

• D

  $\frac{4\mathrm{T}}{{\mathrm{\rho v}}^2}$