Explain how surface tension can be measured experimentally.

1.	Explain how surface tension can be measured experimentally.
Answer» Solution :To find surface tension of a liquid in laboratory TORSIONAL BALANCE is used. It is as shown in figure. It consists of a movable metallic rod fixed on a stretched wire. The position or rod can be adjusted. A glass PLATE is attached at one end of the rod and weight's pan is connected at the other end of the rod. PROCEDURE: A cleaned glass plate is taken. Its length 'l' and thickness 't' is measured . Since thickness t is very small when compared with length 'l', thickness 't' is ignored. Glass plate is fixed to metallic rod. Necessary weights are PLACED in the pan and glass plate is made horizontal to the table. Weights in pan `W_0` is measured. Pure liquid whose surface tension is to be determined is taken in a glass beaker. the liquid is poured until it just touches the glass plate. Now plate is pulled down with some force due to surface tension of liquid. Weights in the pan are gradually increased until the glass plate is just escaped from forces of surface tension. Weights `W_1` are noted. the experiment is repeated for three to four times and average weight `W_1` is noted Surface tension T=`("Force")/("length")` `=((W_1-W_0)=W)/(l e ng th of glass plate i n) ` contact with liquid (2l) `therefore` Surface tension T=`W/(2l)` is measured.

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