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

• A. \(25\)
• B. \(30\)
• C. \(35\)
• D. \(40\)

Hint:

Excess pressure in a soap bubble is 4T/r.

Answer 1

The Correct Option is B

Step 1: Think in terms of surfaces:
Each surface contributes $\frac{2T}{r}$ to the pressure difference, and there are two surfaces.

Step 2: Total:
$\Delta P = \frac{2T}{r} + \frac{2T}{r} = \frac{4T}{r}$.

Step 3: Numbers:
$48 = \frac{4T}{2.5}$, so $T = \frac{48\times2.5}{4} = 30$ dyne/cm.

Final Answer:
T is 30 dyne per cm, option (B). \[ \boxed{30\text{ dyne/cm}} \]