Q 11-09-039JEE MainJEE Main 2026 (24 Jan, Shift 2)Medium
A soap bubble of surface tension $0.04\ \text{N/m}$ is blown to a diameter of 7 cm . If $(15000 - x)\mu\text{J}$ of work is done in blowing it further to make its diameter 14 cm , then the value of $x$ is
______ .
$(\pi = 22/7)$
Numerical value type. Enter your answer.
Answer: 11304
A soap bubble has two surfaces, so $W = T\times2\times4\pi(r_2^2 - r_1^2)$ with $r_1 = 3.5$ cm, $r_2 = 7$ cm.
$$W = 0.04\times8\times\frac{22}{7}\times\left(0.07^2 - 0.035^2\right) = 0.04\times8\times\frac{22}{7}\times0.003675$$
$$W = 3.696\times10^{-3}\ \text{J} = 3696\ \mu\text{J}$$
$$15000 - x = 3696\Rightarrow x = 11304$$
Solution by Sreeraj P, M.Sc Physics