Question

The surface tension of a liquid is $5$ Newton per meter. If a film of this liquid is held on a ring of $0.02$ $meter{s}^2$. Its surface energy is about

• A. $5J$
• B. $2J$
• C. $0.2J$
• D. $3J$

Answer 1

The correct option is C $0.2J$

Given$-$

$T=5N/m$

$A=0.02m^2$

As soap film will be formed at both sides of ring$,$

Area $=2A$

Surface energy is calculated by $-$

Surface energy $=$ Surface tension $\times$ area

$E=T\times 2A$

$E=5\times 2\times 0.02$

$E=0.2J$

Surface energy is therefore $0.2J.$

Hence,

option $\left(C\right)$ is correct answer.