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Home » Figure (a) shows a thin liquid film supporting a small weight = 4.5 × 10–2 N. What is the weight supported by a film of the same liquid at the same temperature in Fig. (b) and (c)? Explain your answer physically.
Figure (a) shows a thin liquid film supporting a small weight = 4.5 × 10–2 N. What is the weight supported by a film of the same liquid at the same temperature in Fig. (b) and (c)? Explain your answer physically.
CBSE | Class 11 | Mechanical Properties of Fluids | NCERT | Physics
Figure (a) shows a thin liquid film supporting a small weight = 4.5 × 10–2 N. What is the weight supported by a film of the same liquid at the same temperature in Fig. (b) and (c)? Explain your answer physically.

Answer :

(a) According to the question, the length of the film which is supporting the weight is

= 40 cm = 0.4 m.

and the total weight supported = 4.5 x 10-2 N.
We know that the film has two free surfaces. Therefore, Surface tension becomes

S = 4.5 x 10-2/2 x 0.4

S = 5.625 x 10-2 Nm-1
Since the temperature and the liquid is the same for all the given cases (a), (b), and (c), therefore surface tension for cases (b) and (c) will also be the same, i.e., = 5.625 x 10-2.

The length of the film supporting the weight in Figs. (b) and (c) is the same as in (a), hence the total weight supported in each case is qwerty.

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