JEE Mains · Physics · STD 11 - Surface tension
- JEE Mains 2026
- Medium
- Numerical
The surface tension of a soap solution is \(3.5 \times 10^{-2}\) N/m. The work required to increase the radius of a soap bubble from \(1\) cm to \(2\) cm is \(\alpha \times 10^{-6}\) J. The value of \(\alpha\) is _____. (\(\pi = 22/7\))
Pick an option to check your answer.
Answer & Solution
Correct Answer
(C) 264
Step-by-step Solution
Detailed explanation
The work done to increase the radius of a soap bubble is given by \(W = T \times \Delta A\)
Since a soap bubble has two free surfaces, the change in surface area is \(\Delta A = 2 \times 4\pi (r_2^2 - r_1^2)\)
Substituting the given values:
\(W = 3.5 \times 10^{-2} \times 8\pi \times ((2 \times 10^{-2})^2 - (1 \times 10^{-2})^2)\)
\(W = 3.5 \times 10^{-2} \times 8\pi \times (4 \times 10^{-4} - 1 \times 10^{-4})\)
\(W = 3.5 \times 10^{-2} \times 8\pi \times 3 \times 10^{-4}\)
\(W = 84\pi \times 10^{-6}\)
Using \(\pi = \dfrac{22}{7}\):
\(W = 84 \times \dfrac{22}{7} \times 10^{-6} = 264 \times 10^{-6}\) J
Comparing with \(\alpha \times 10^{-6}\) J, we get \(\alpha = 264\)
Answer: \(264\)
Since a soap bubble has two free surfaces, the change in surface area is \(\Delta A = 2 \times 4\pi (r_2^2 - r_1^2)\)
Substituting the given values:
\(W = 3.5 \times 10^{-2} \times 8\pi \times ((2 \times 10^{-2})^2 - (1 \times 10^{-2})^2)\)
\(W = 3.5 \times 10^{-2} \times 8\pi \times (4 \times 10^{-4} - 1 \times 10^{-4})\)
\(W = 3.5 \times 10^{-2} \times 8\pi \times 3 \times 10^{-4}\)
\(W = 84\pi \times 10^{-6}\)
Using \(\pi = \dfrac{22}{7}\):
\(W = 84 \times \dfrac{22}{7} \times 10^{-6} = 264 \times 10^{-6}\) J
Comparing with \(\alpha \times 10^{-6}\) J, we get \(\alpha = 264\)
Answer: \(264\)
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