A small piece of wire of length 4 cm is floating on the surface of water. If a force of 560 dynes in excess of itss apparent weight is requried to pull it up from the surface find the surface tension of water.

Explanation

Length of wire `l=4cm` contact length of solid with liquid surface `L=2l=8cm`. Surface tension
`T=(F)/(L)impliesT=(560)/(8)=70"dyne"//cm`
`T_("water")=70"dyne" cm^(-1)=0.07Nm^(-1)`