Question

Assertion: Droplets of liquid are usually more spherical in shape than large drops of the same liquid.
Reason: Force of surface tension predominates the force of gravity in case of small drops.
A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Assertion is correct but Reason is incorrect.
D) Assertion is incorrect but the reason is correct.

Answer 1

Hint: Droplets have different shapes. This is because of the effect of the forces acting on the drop. The force which dominates other forces will decide the shape of the drop. So here first take a look into the total forces acting on the drop and the effect of those forces.

Complete step by step answer:
There are two factors on which the shape of a liquid drop depends:
(1) Surface Tension
(2) Gravitational Force
There will be two cases.
Case I: When Gravitational Force is greater than Surface Tension:
Due to the gravitational force, the molecules of the drop will experience a downward force. Whereas, due to surface tension the particles of the drop will try to reduce the surface area of the drop. Since the gravitational force is greater than surface tension, so in this case, the shape of the drop will not be spherical. It will be in an oval shape. The size of the drop will be large.
Case II: When Surface Tension is greater than Gravitational Force:
Since surface tension is greater than gravitational force; due to surface tension the molecules of water droplets will exert a large force of attraction in order to reduce the surface area, therefore, the size of the water droplet will be spherical.

Hence, option (A) is the correct answer.

Additional information:
Always place the object on the left of the mirror and place the mirror at the origin. Since the incident beam direction is from left to right so any distance measured in the right side of the mirror will be positive and any distance measured in the left will be negative. Notice, now the sign convention is just the same as that of the Cartesian coordinate system.

Note:
Some of these types of problems can be solved by recalling the concept of surface tension and gravitational force and also the factors on which these forces depend. What is the effect of density, volume, etc. of a liquid on its surface tension.