Question
Physics Question on 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 Nm-1, then the excess force required to take it away from the surface is :
A
19.8 mN
B
198 N
C
1.98 mN
D
99 N
Answer
19.8 mN
Explanation
Solution
Excess force is calculated as:
F = 2πr · T = 2π(0.045)(0.07) = 19.8 mN.