Understanding Surface Tension and the Role of Force in U-Shape Wire Frames

[AdityaDev]

If I have a U-shape wire frame and it contains a straight sliding wire and I dip this in soap, a film forms between the sliding wire and the boundary of U shape frame. Why is the force due to surface tension F = 2Tl where l is length of sliding wire?

They say there are 2 layers in contact. Which 2? There is only one film.

Also
$dW=Fdx=(2Tl)dx$
They book says 2ldx is the change in area dA. Why?
$dW = Tdx$
$hence, T= dW/dA$

 

[Bystander]

How many sides does the film have?

 

[AdityaDev]

How many sides does the film have?

4 sides. 1 stuck withe the slider. 3 bounded by frame.

 

[Bystander]

Not edges --- sides?

 

[Chestermiller]

The film has two surfaces. There is surface tension on each surface.

Chet

 

[AdityaDev]

Not edges --- sides?

Understood. 2 surfaces.
Thank you

 

[gracy]

Understood. 2 surfaces.
Thank you

T
One surface and then flipping this vertically

in this way two surfaces.Each surface has surface tension so F = 2Tl.