Question

A square wire frame of side 'L' is dipped in a liquid. On taking it out a membrane is formed. If the surface tension of liquid is T, the force acting on the liquid surface will be?

• A. 4 TL
• B. 10 TL
• C. 2 TL
• D. 8 TL

Answer 1

The correct option is D

8 TL

Perimeter of square is 4L on one side.

So total length {including upper face and lower face) = 8L

As you know, S=$\frac{F}{L}$
$\Rightarrow T=\frac{F}{8L}$
F=8TL

So the liquid film is pulling the wire frame towards itself by F = 8TL

And from newton's (III) law,

Wire frame is pulling the liquid towards itself by same magnitude of force i.e., 8 TL