Question

Surface tension of a liquid is 5 N/m. If its thin film
is made in a ring of area 0.02 m², then its surface
energy will be
-
(1) 5x 10-2 Joule
(2) 2.5 x 10-2 Joule
(3) 3 x 10-1 Joule
(4) 2 x 10-1 Joule​

Answer 1

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 × 5 × 0.02J

=0.2J =2 × 10-¹

hence, option 4 is the right answer