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 :

Answer

2

Explanation

Surface energy is related to the surface tension by the relative ` U = TA `
Given ` T = 5 N m ^ -1 `
Area ` = 2 A = 2 xx 0.02 = 0.04 m ^ 2 therefore U = 5 xx 0.04 = 0.20 J = 2 xx 10 ^(-1) J `