Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

Solutions (^229)
Water is kept in the capillary by surface tension.
If ph is the surface tension at the temperature Th,
we can write
2crh
pwgr
where pw is the density of water. Hence we obtain
Q
pgrh pgrl Th
h (^2) 2 / Tup i•
Using the hint in the conditions of the problem,
we plot the graph of the function (I (T). The tem-
perature Th on the level of the maximum ascent
80 -
50
40
20
0 20 40
60 80
Fig. 202
of water is determined by the point of intersection
of the curves describing the (pgr112) TIT„p and
u (T) dependences. Figure 202 shows that Th
80 °C. Consequently,
1T h
h - 6.4 cm.
u p
The problem can also be solved analytically
if we note that the a (T) dependence is practically
linear.