Calculating the surface tension using the method of Lecomt de Nouy

AI Thread Summary
The discussion revolves around calculating surface tension using the Lecomte de Nouy ring method. The initial calculation yielded a surface tension value of 0.22 N/m, which was incorrect compared to the expected 0.1016 N/m. The mistake was identified as a misinterpretation of the force formula, specifically confusing mass with weight. After clarifying that the force should include the weight of the ring (mg), the correct calculation was achieved. The participant acknowledged the error and expressed gratitude for the assistance received.
arhzz
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Homework Statement
The surface tension can be determined using the Lecomte De Noüy ring method. The mass of the ring is m = 4.9 g and the diameter d = 64.1 mm. The tensile force just before tearing is in water at 25 ° C is F = 0,089 N. Calculate the surface tention
Relevant Equations
y = F/4*pi*r
Hello! I am having unexpected difficulties with this problem.A friend showed me an article regarding the Lecomde ring method,and at the bottom was this little problem that to solve.I've done it like this.

$$ y = \frac{F}{4\pi r} $$ where F is the given force and r is = 0,0325 in meters. The value I get is y = 0,22 N/m. But according to the solutions this is wrong,the right solution should be y = 0,1016 N/m.I highly doubt they are wrong,which means I made a mistake somewhere but I don't see where.The only formula that appered in the article was this and the usual surface tension.What am I i missing here.Thank you!
 
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You are given the mass of the ring. Does the force you are given include the weight of the ring?
 
arhzz said:
Homework Statement:: The surface tension can be determined using the Lecomte De Noüy ring method. The mass of the ring is m = 4.9 g and the diameter d = 64.1 mm. The tensile force just before tearing is in water at 25 ° C is F = 0,089 N. Calculate the surface tention
Relevant Equations:: y = F/4*pi*r

What am I i missing here.
You are misinterpreting the formula. The one here gives the expected answer and explains how the terms are put together.
 
Last edited:
Okay so I've tried using the formula where the mass of the ring is take into account.

$$ F = m + 4
\pi * r * y $$

If I try to get y out of this it should look like this; $$ y =
\frac{F-m}{4
\pi r} $$

But I still do not get the wanted result.
 
The weight is ##mg## not ##m##.
 
kuruman said:
The weight is ##mg## not ##m##.
Ohh,it said wait not mass,my bad I didnt read carefully.Now I get the right result,sorry for the silly mistake and thank you for your help!
 
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