Question

The rain drops are spherical shape due to
(a) Surface tension
(b) Viscosity
(c) Residual pressure
(d) Thrust on drop

Answer 1

Hint: We will solve this sum by defining all the terms and then on the basis of definition we will apply trial and error methods. Then based on that we will find the reason due to which rain drops are spherical in shape.

Complete step-by-step solution -
In question we are asked to find the reason for the spherical shape of water droplets. So, first of all we will define each and every term,
Surface tension: Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. As the cohesive force, molecules are pulled towards each other equally in every direction, so due to that the resulting or net force remains zero and the shape can be maintained easily.
Viscosity: It is the property of any liquid that resist the liquid to slide on any surface. The force acting in the opposite direction of the sliding force is called viscous force. The shape of the liquid or molecules may deform.
Residual pressure: It is pressure that acts on the pipe when water is flowing through it. It does not depend on the shape of an individual molecule of water.
Thrust on drop: It is also a force acting on the drop when it is sprinkled or sprayed from pipe or anything else. This quantity also does not refer to a single molecule.
Now, considering all the definitions it can be said that the spherical shape of a molecule is due to surface tension acting inside the molecule as well as acting outside due to air.
Thus, option (a) is the correct answer.

Note: In surface tension two primary mechanisms are responsible i.e. inward force on surface molecules which causes the liquid to contract and the other is tangential force which is parallel to the surface of liquid. Here, we have considered only inner force on the molecules but tangential force can also be considered for solving the problem.