Abstract:
Light diffraction by capillary waves, generated on the surface of a liquid is a
very precise and none destructive method of finding the surface tension and
other related physical parameters. In this research diffracted laser light
patterns formed by the generation of surface capillary waves were used to
find the surface tension of distilled water and the interfacial tension between
thin kerosene films floating on distilled water as a function of film
thickness. A pin attach to the diaphragm of a speaker was served as the
exciter to generate surface capillary waves by the center of a dish which
was filled with distilled water up to a certain level. A semiconductor laser
(wavelength = 660 nm) was used as the coherent light source for the
experiment. The diffracted light from the liquid surface was obtained on to
a distant vertical wall, which served as the screen for the experiment. The
diffraction patterns were observed by changing the oscillating frequency of
the exciter pin. Obtained value of surface tension for distilled water was
recorded as (0.0766
±
0.0015) Nm-1
. By adding known amount of kerosene
and following the same procedure the interfacial tension was calculated for
several thicknesses (0.07, 0.14 and 0.21 mm) of kerosene film as
0.0470
±
0.0022, 0.0404
±
0.0025 and 0.0362
±
0.0010 Nm-1
. The sudden
drop in interfacial tension even for a slight kerosene film is observed and
further study of film thickness against interfacial tension is proposed to
model the effect of kerosene on natural water resources.
