10.18 Figure 10.24 (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.
The length of the liquid film supported by the weight, l = 40 cm = 0.4 m
The weight supported by the film, W = 4.5 N
Since a liquid film has two free surfaces,
Surface tension = = = 5.625 N/m
In all 3 figures, the liquid is the same, temperature is also the same. Hence the surface tension in (b) and (c) are also going to be the same, with the value of 5.625 N/m and weight supported in each case is also going to be the same, since length of the film is same.
<div><div>Let us take the case (a):</div></div><p>The length of the liquid film supported by the weight, l = 40 cm = 0.4 m</p><p>The weight supported by the film, W = 4.5 <span title="Click to copy mathml"><math><mo>*</mo><msup><mrow><mrow><mn>10</mn></mrow></mrow><mrow><mrow><mo>-</mo><mn>2</mn></mrow></mrow></msup></math></span> N</p><p>Since a liquid film has two free surfaces, </p><p>Surface tension = <span title="Click to copy mathml"><math><mfrac><mrow><mrow><mi>W</mi></mrow></mrow><mrow><mrow><mn>2</mn><mi>l</mi></mrow></mrow></mfrac></math></span> = <span title="Click to copy mathml"><math><mfrac><mrow><mrow><mn>4.5</mn><mi mathvariant="normal"></mi><mo>*</mo><msup><mrow><mrow><mn>10</mn></mrow></mrow><mrow><mrow><mo>-</mo><mn>2</mn></mrow></mrow></msup></mrow></mrow><mrow><mrow><mn>2</mn><mo>*</mo><mn>0.4</mn></mrow></mrow></mfrac></math></span> = 5.625 <span title="Click to copy mathml"><math><mo>*</mo><msup><mrow><mrow><mn>10</mn></mrow></mrow><mrow><mrow><mo>-</mo><mn>2</mn></mrow></mrow></msup></math></span> N/m</p><p>In all 3 figures, the liquid is the same, temperature is also the same. Hence the surface tension in (b) and (c) are also going to be the same, with the value of 5.625 <span title="Click to copy mathml"><math><mo>*</mo><msup><mrow><mrow><mn>10</mn></mrow></mrow><mrow><mrow><mo>-</mo><mn>2</mn></mrow></mrow></msup></math></span> N/m and weight supported in each case is also going to be the same, since length of the film is same.</p>
Bernoulli's principle states that in a steady flow, the sum of pressure, kinetic energy per unit volume, and potential energy per unit volume remains constant.
Yes, the Mechanical properties of fluids class 11th physics is important in NEET. On average, 1-2 questions would be asked from this chapter, which you can cover from the Class 11th Mechanical Properties of Fluids notes.
The main mechanical properties of fluids are exerting pressure, resisting flow or viscosity, forming surface tension, following Bernoulli's principle, and moving in a streamline.
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