MCQ
Q.
If we increase the temperature of fluid its surface tension will_________.
Correct Answer: C
CONCEPT:
- It is the property of liquid by virtue of which the free surface of the liquid at rest acting like a stretched membrane trying to contract to reduce its surface area.
- Surface tension is a force per unit length (or surface energy per unit area) acting in the plane of interface between the liquid and the bounding surface.
- It is the extra energy that the molecules at the interface have as compared to the interior.
- The surface tension is the force acting perpendicular on a unit length of an imaginary line drawn on the surface of the liquid and it can be expressed as
\(\Rightarrow T = \frac{F}{l}\)
- Because of this surface tension, few insects can easily float on liquid surface similarly a needle can be made to float on the surface of liquid using this principle
Here,
T = surface tension,
F = force acting on the surface (Cohesive force)
l = unit length
EXPLANATION:
- As explained above, the surface tension acting on a fluid surface can be expressed as
Surface tension, \(T = \frac{{{\rm{The\;cohesive\;force\;between\;molecule}}}}{{unit\;length}}\)
- Also, we know that cohesive force or the attractive force between the liquid molecules is inversely proportional to its temperature.
- Since as we increase the temperature of fluid its interatomic distance will keep on increasing hence it will cause a decrease in the surface tension of the fluid.
i.e., \(surface\;tension,\;T \propto \frac{1}{{temperature}}\)
So, only option 3rd is correct.
