Question

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

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

Answer 1

The correct option is C $8TL$

As the square frame has $4$ sides and the membrane has two surfaces:

Force acting on one side$\left(F\right)=$ surface tension$\times$ Length $=$TL

So force acting on $4$ sides $=4\times F=4TL$

For both surfaces the net force on the square frame $=2\left(4TL\right)=8TL$.