Question

A thin square plate of side 5 cm is suspended vertically from a balance so that the lower just dips into water with side parallel to surface. When the plate is clean (angle of contact it appears to weight 0.044 N.) But when the plate is greasy (angle of contact ${180}^0$), it appers weight 0.03 N. Then the surface tension of water is

Answer 1

$\cos 0.2l-T\cos 180.2l=0.044-0.03$

$2.T.2l=0.014$

$T\times 4\times 0.05=0.014$

$T=7\times {10}^{-2}N$