Question

Figure (a) shows a thin liquid film supporting a small weight = 4.5 x 10^-2 N. What is the weight supported by a film of the same liquid at the same temperature in figure (b) and (c)? Explain your answer physically.

Answer 1

As shown in the fig.(a)

Length, l = 40 cm = 40 x 10^-2 m

Also, Force, F = 4.5 x 10^-2 N

surface tension, T = F/2l = {4.5 x 10^-2}/{2 x 40 x 10^-2} = 5.625 x 10^-2 Nm^-1

In case of figures (b) and (c), length is again 40 x 10^-2 m

Small weight that the film can support is

F = T x (2l) = 5.625 x 10^-2 x 2 x 40 x 10^-2

= 4.5 x 10^-2 N