Question

A square wire frame of size $L$ is dipped in a liquid. On taking out, a membrane is formed. If the surface tension of liquid is $T$, then force acting on a frame will be

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

Answer 1

The correct option is C $8TL$

Perimeter of square wire frame $=4\times L$.
As soap film has two interfaces.
$\therefore$ Length of wire on which surface tension force is acting $=2\times (4\times L)=8L$
We know,
$T=\frac{F}{L_{Total}}$

$\Rightarrow F=T\times \left(8L\right)=8TL$