Question

A wire ring of internal radius
3cm and external radius 3.2 cm is
rested on the surface of a liquid and
then raised. An extra pulling force
equivalent to the weight of 3.03g is
required before the film breaks than it
is after. Calculate the surface tension
of the liquid.

Answer 1

Internal radius of wire, r = 3cm

external radius of wire, R = 3.2 cm

we know, effective length , L = 2π(r + R)

L = 2 × 3.14 × (3 + 3.2) × 10^-2 m

L = 6.28 × 6.2 × 10^-2 m

L = 0.389 m


force , F = mg = 3.03g × 10m/s²

= 3.03 × 10^-3 × 10 = 0.03N

now, surface tension, S = F/L = 0.03/0.389

S = 0.0771 N/m