Question-19 A liquid drop of volume V is placed on the surface of glass plate. Then another glass plate is placed on it such that liquid forms a thin layer of area A between the surfaces of two plates. To separate the plates a force F has to be applied normal to the surfaces. The surface tension of the liquid is
(A) \frac{FV}{2A}
(B) \frac{FV}{2A^2}
(C) \frac{FV}{A^2}
(D) \frac{F}{VA}
Answer : (B)
Explanation:
Force (F) = \frac{2TA}{t}=\frac{2TA^2}{V}
….(∵ t=\frac{V}{A} = Thickness of the layer)
∴ T=\frac{FV}{2A^2}