Question

A number of small drops of mercury adiabatically coalesce to form a single drop. The temperature of the drop will
A. increase
B. remain same
C. decrease
D. depend on size

Answer 1

First we need to know what happens in an adiabatic process. In this process the heat produced cannot be released by the body due to which it creates a temperature change. Then assume the given condition and analyze the product that is released from this process, then apply adiabatic conditions to find the correct option.

Complete answer:
Adiabatic process: In thermodynamics we can say that adiabatic process is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. This process transfers energy to the surroundings only as work.

Now as per the problem a number of small drops of mercury adiabatically coalesce to form a single drop. We need to find out what will happen to the temperature of the big drop.Let us first assume this given statement in an opposite direction, that we have a big single drop and we need to break it into a number of small drops. Then some amount of work must be done on the single drop so as to break it into small drops.

And this work is stored in the form of potential energy and hence small drops have more potential energy. Now if we combine this small small drop having some potential energy then after combination it will release some potential energy while forming a single drop at the same time heat is also released.But in the problem it is given that the process is adiabatic hence heat will not release from this combination that is why the temperature of the single drop increases.

Therefore the correct option is (A).

Note: Keep in mind that no doubt in an adiabatic process no heat transfer takes place between its environment , this does not mean that the temperature is constant but rather that no heat is transferred into or out from the system. These adiabatic changes are usually accompanied by changes in temperature.