Question

The surface tension of a liquid is $5N/m$ If a film is held on a ring of area $0.02m{s}^2$ its surface energy is about

• A. $5\times {10}^{-2}J$
• B. $2.5\times {10}^{-2}J$
• C. $2\times {10}^{-1}J$
• D. $3\times {10}^{-1}J$

Answer 1

Answer: (C)

$2\times {10}^{-1}J$

Since there are two surfaces of equal area formed on a ring, the total surface energy of the film is given by

$E=2TA=2\times 5\times 0.02J$

$=0.2J=2\times {10}^{-1}J$