A thin circular ring of radius 3.5 cm is resting horizontally on the surface of a liquid. If the surface tension of the liquid is 0.05 N m ⁻¹ , the excess upward force required to detach the ring completely from the surface is

Step-by-step solution

Given: Radius of the ring, R = 3.5 cm = 3.5 10⁻² m Surface tension, T = 0.05 N m ⁻¹ When a thin circular ring rests on a liquid surface, the liquid is in contact with both its inner and outer circumferences. Total length of contact, L = 2 R + 2 R = 4 R The excess upward force required to detach the ring is equal to the force due to surface tension. F = T L = T 4 R Substituting the values: F = 0.05 4 22 7 3.5 10⁻² F = 0.2 22 0.5 10⁻² F = 2.2 10⁻² N F = 22 10⁻³ N = 22 mN Answer: 22 mN