Question

Which of the following are not true about the surface tension?
A. Small Liquid Drop take spherical shape due to surface tension
B. Surface tension is a vector quantity
C. The surface tension of a liquid is a molecular phenomenon
D. The surface tension of liquid depends on length but not on the area

Answer 1

Hint: The surface tension is a quantity that does not have any particular direction and it is called a scalar and it depends on the force acting on the surface per unit length. Here we need not consider the direction of the length taken.

Complete step-by-step answer:
What is surface tension?
Surface tension is the tendency of the fluid to arrange itself into a shape of minimum possible surface area.
For example, we have seen the rain droplets always in the shape of the sphere which is because of the surface tension. The sphere is the shape that has the least possible surface area.
Another example is that when we see a thermometer broken the mercury drops will have a curved edge when it comes in contact with the ground. This is due to the highest surface tension of the Mercury
Surface tension is the phenomenon that occurs when the surface of a liquid is in contact with another phase (it can be a liquid as well). Liquids tend to acquire the least surface area possible. The surface of the liquid behaves like an elastic sheet.
Surface tension is the phenomenon that occurs at the molecular level. It is the force per unit length by which the bulk of the liquid attracts the surface molecules and makes them occupy the minimum surface area.
Hence we have understood the surface tension is a molecular phenomenon.
Now we can mathematically express the surface tension as the force acting on the surface per unit length of the surface.
$T = \dfrac{F}{L}$
Here we only consider the magnitude of the force and not the direction of the force.
Now consider the given options
The first option can be eliminated because the surface tension is the reason behind the spherical shape of the droplets of the rain.
The surface molecules are attracted by the inner molecules and hence they are forced to form a min surface area or spherical shape.

The second option says that the surface tension is a wrong vector quantity. The surface tension, though dependent on the force, has nothing to do with the direction of the force. So the surface tension is the magnitude of the force per unit length.

The third option says that the surface tension is a molecular phenomenon.
As we have already discussed, the phenomenon occurs at the molecular level and the molecules of the surface are attracted by the molecules in the bulk and forced to form a min surface area.

The fourth option says that the surface tension is dependent on the length and not on the area which is correct from what we have discussed earlier that the surface tension is the force per unit length.

Note: The surface tension is dependent on the force and length and immediately one may think it is a vector quantity because of the force. But it is not, one has to understand that surface tension is dependent on the magnitude of the force and not on the direction of the force.