Question

The surface tension of a liquid is `5` Newton per metre. If a film is held on a ring of area `0.02 metres^(2)`, its surface energy is about :
A. `2 xx 10^(-2) J`
B. `2.5 xx 10^(-3) J`
C. `2 xx 10^(-1) J`
D. `3 xx 10^(-1) J`

Answer 1

Correct Answer - C
Surface energy is related to the surface tension by the relation, `U = Delta A`
Given, `T = 5 Nm^(-1)`
`Delta A = 2A = 2 xx 0.02 = 0.04 m^(2)`
`:. U = 5 xx 0.04 = 0.20 J = 2 xx 10^(-1) J`