Question

A square frame of side $l$ is dipped in a liquid soap. When it is taken out of the liquid, a film is formed on it. If surface tension is $T$ then force acting on it is

• A. $2Tl$
  
• B. $4Tl$
  
• C. $8Tl$
  
• D. $16Tl$
  

Answer 1

The correct option is C $8Tl$

Net force acting on it = 2(force on one surface)

= 2$\times T\times \left(perimeter\right)$

= $2\times T\times 4l$

$Netforceactingonthesquareframe=8Tl$