The surface tension of a liquid is 5 newton per metre. If a film is held on a ring of area 0.02 metre², its surface energy is about

Options

(a) 5×10⁻² J
(b) 2.5×10⁻² J
(c) 2×10⁻¹ J
(d) 3×10⁻¹ J

Correct Answer:

2×10⁻¹ J

Explanation:

Surface tension = Surface energy/Surface Area
Since the film has two surface
.·. Surface energy = (5 Nm⁻¹) (2 x 0.02 m²) = 2 x 10⁻¹ J.