Question

When a cylindrical tube is dipped vertically into a liquid the angle of contact is\[{140^ \circ }\]. When the tube is dipped with an inclination of\[{40^ \circ }\], the angle of contact is.

Answer 1

Hint: We are first going to take the angle of contact that is given in the question. After that, we will analyze the tube when it is dipped inside the liquid with an inclination of the angle of\[{40^ \circ }\]. We will see whether the angle of contact when it is dipped inclined, depends upon the angle of inclination or not.

Complete step-by-step solution:
It is given in the question that the angle of contact when the tube is dipped in it is: \[{140^ \circ }\]
If we take a container in which liquid is filled, and a capillary tube is dipped in it then liquid rises:
Let the height up to which the liquid rises in the tube: \[h\]
Now weight is balanced by surface tension. Now if the tube is kept inclined in the liquid, then the height will remain\[h\], the slant height will be different. Thus, the pressure in the tube will be the same as the atmospheric pressure and also, both the surface meniscus are the same. Now if the meniscus is the same, the angle of contact will also be the same. Which means that the angle of contact is independent of the angle of inclination.
So, the angle of contact when the tube is inclined is the same as that of the vertical dipping, i.e., \[{140^ \circ }\].

Note: It is important to note that the angle of contact of the tube when it is inclined at an angle does not depend on the angle of inclination but the level of the meniscus. It can be observed that the level of the meniscus is the same for both the cases. Thus, the angle of contact is also the same.