# 18. Class 11th Physics | Surface Tension | Solved Example-5 on Surface Tension | by Ashish Arora in this example we are given that a liquid
of specific gravity one point five is observed to rise three centimeter in a cap-illary tube.
of diameter point five m-m. and the liquid wets the surface of the tube . and we are
require to calculate the excess pressure inside a spherical bubble of one centimeter diameter
blown from the same liquid. and it is given that the angle of contact is zero degree and
we need to take g as ten meters per second square. so here we can use, as we know. the
surface tension. of a liquid is given as. here we can directly use the. expression for
cap-illary action. so the surface tension can be written as . r h ro g by twice of coz
theta . where the symbols are having usual meanings. if we substitute the values the
radius of, the cap-illary tube is , half of point five m-m it is zero point two five into
ten to power minus three . and it is given that , the cap-illary height is three centimeter
so it is three into ten to power minus two, the density of. water we can take as thousand.
and g we can take as . ten. and the specific gravity is one point five so density of liquid
will be one point five into thousand . divided by . twice of coz zero we can take as one
if we just simplify this . numerical value it will give us fifty-six point two five into
ten to power minus three newton per meter that’s the surface tension of the liquid
which , we have calculated buy using. the expression for cap-illary action. and now
using this we can easily find out the excess pressure. inside. the bubble. this can be
given as excess pressure we know it is equal to four t by r. so as the value of surface
tension we are having . is four multiplied by fifty-six point two five into ten to power
minus three divided by, the radius of soap bubble where it is given that it is one centimeter
in diameter so this will be point five into ten to power, minus two. on calculation this
will give us. simply it is forty-five pascle, that will be the answer to our problem.

### 2 Replies to “18. Class 11th Physics | Surface Tension | Solved Example-5 on Surface Tension | by Ashish Arora”

1. Sai Srikar Gollamudi says:

Sir what is the significance of the point 'the liquid wets the surface' and why is excess pressure not 2t/r.

2. vandana vyas says:

Sir, I have a doubt-
How can the liquid level rise if the angle of contact is zero degree???