- #1
huyhohoang
- 12
- 0
Member advised to use the homework template!
Hi everybody, I now encounter some problems when try to solve this:
Problem statement: Calculate the work done to blow a soap bubble to radius R. Knowing that the process is isotherm, the atmospheric pressure is H, the surface tension is γ.
Solution:
$$A = A_{1}+A_{2}$$
In which A1 is the work done to blow the bubble with 2 layers :
$$A_{1} = 2(4 \gamma πR^{2}) $$
A2 is the work done to blow the bubble to pressure p' = H + 4γ/R
$$A_{2}=p' V ln \dfrac{p'}{H}$$
The solution above is in my textbook, but I still help some questions
First, why the soap bubble has 2 layers, which leads to the Laplace pressure is 4γ/R?
Secondly, in A2 equation, why the ratio is natural logarithm is p' over H? In the isotherm, we have: $$\dfrac{V_{i}}{V_{f}}=\dfrac{p'}{H}$$
It doesn't match the formula used to calculate work done in the isotherm process.
Can anyone explain these problems in details for me?
Thanks a lot.
Problem statement: Calculate the work done to blow a soap bubble to radius R. Knowing that the process is isotherm, the atmospheric pressure is H, the surface tension is γ.
Solution:
$$A = A_{1}+A_{2}$$
In which A1 is the work done to blow the bubble with 2 layers :
$$A_{1} = 2(4 \gamma πR^{2}) $$
A2 is the work done to blow the bubble to pressure p' = H + 4γ/R
$$A_{2}=p' V ln \dfrac{p'}{H}$$
The solution above is in my textbook, but I still help some questions
First, why the soap bubble has 2 layers, which leads to the Laplace pressure is 4γ/R?
Secondly, in A2 equation, why the ratio is natural logarithm is p' over H? In the isotherm, we have: $$\dfrac{V_{i}}{V_{f}}=\dfrac{p'}{H}$$
It doesn't match the formula used to calculate work done in the isotherm process.
Can anyone explain these problems in details for me?
Thanks a lot.