2024 Mechanical Properties of FluidsSurface Tension Medium Question 2 of 3 in Surface Tension

A thin flat circular disc of radius 4.5 cm is placed gently over the surface of water. If surface tension of water is 0.07 N m$^{-1}$, then the excess force required to take it away from the surface is;

A 1.98 mN
B 99 N
C 19.8 mN
D 198 N

The answer is C.

Solution

Excess force required $F = (2\pi R)T$ $= 2\pi \times 4.5 \times 10^{-2} \times 0.07$ $= 9\pi \times 7 \times 10^{-4} = \frac{63\pi}{10}$ mN $\approx 19.8$ mN

Concept Force required to detach a disc from a liquid surface

Surface Tension in past papers

3 questions from this chapter have appeared across 3 exam years.