A thin circular ring of radius 5 cm is placed gently on the surface of water. If the surface tension of water is 0.07 N m ⁻¹ , the excess force required to lift the ring from the surface is (Take = 22 7 )

Step-by-step solution

For a thin circular ring, both the inner and outer boundaries are in contact with the liquid surface. Total effective length of contact, L = 2 R + 2 R = 4 R Excess force required, F = T L = T 4 R F = 0.07 4 22 7 0.05 F = 0.01 4 22 0.05 = 0.044 N F = 44 mN Answer: 44 mN