21. The surface tension of liquid is 0.5 N/m. If a film is held on a
The surface tension of liquid is 0.5 N/m. If a film is held on a ring of area 0.02 m2, its surface energy is
(a) 5 × 10-2 joule
(b) 2.0 × 10-2 joule
(c) 4 × 10-4 joule
(d) 0.8 × 10-1 joule
Ans. b
(5)