Question:
The excess pressure inside a soap bubble of radius \(2.5\) cm is \(48\) dyne/cm\(^2\). The surface tension of soap solution in dyne /cm is
The excess pressure inside a soap bubble of radius \(2.5\) cm is \(48\) dyne/cm\(^2\). The surface tension of soap solution in dyne /cm is
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Excess pressure in a soap bubble is 4T/r.
Updated On: Oct 1, 2026
- \(25\)
- \(30\)
- \(35\)
- \(40\)
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
A soap bubble has two free surfaces (inside and outside), so its excess pressure is \(\Delta P = \frac{4T}{r}\).
Step 2: Solve for T:
\[ T = \frac{\Delta P\, r}{4} = \frac{48 \times 2.5}{4} = \frac{120}{4} = 30 \text{ dyne/cm} \]
Step 3: Why the other options are wrong.
Using \(\Delta P = \frac{2T}{r}\), which is for a single surface (a liquid drop), would give 60 dyne/cm. Values 25, 35 and 40 do not follow from the formula.
Final Answer:
The surface tension is \(30\) dyne/cm, option (B). \[ \boxed{30\text{ dyne/cm}} \]
A soap bubble has two free surfaces (inside and outside), so its excess pressure is \(\Delta P = \frac{4T}{r}\).
Step 2: Solve for T:
\[ T = \frac{\Delta P\, r}{4} = \frac{48 \times 2.5}{4} = \frac{120}{4} = 30 \text{ dyne/cm} \]
Step 3: Why the other options are wrong.
Using \(\Delta P = \frac{2T}{r}\), which is for a single surface (a liquid drop), would give 60 dyne/cm. Values 25, 35 and 40 do not follow from the formula.
Final Answer:
The surface tension is \(30\) dyne/cm, option (B). \[ \boxed{30\text{ dyne/cm}} \]
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