Question

Two identical blocks of iron, one at ${10}^{\circ }\mathrm{C}$ and the other at ${20}^{\circ }\mathrm{C}$, are put in contact. Suppose the cooler block cools to $5^{\circ }\mathrm{C}$ and the warmer block warms to ${25}^{\circ }\mathrm{C}$. This would violate which law of thermodynamics?

• A. Zeroth Law of thermodynamics
• B. First Law of Thermodynamics
• C. Second Law of Thermodynamics
• D. Third Law of Thermodynamics

Answer 1

The correct option is A

Zeroth Law of thermodynamics

Explanation for correct option:

Zeroth law of thermodynamics

1. According to the zeroth law of thermodynamics, when two objects are kept in contact, the heat flows from the hotter body to the cooler body until they reach equilibrium.
2. Here, the cooler block cools more, and the hotter block gets hotter.
3. In order to achieve thermal equilibrium, the temperature of the hotter block needed to be reduced to ${15}^{\circ }\mathrm{C}$.
4. Meanwhile, the temperature of the cooler block would have reached to${15}^{\circ }\mathrm{C}$.
5. This means the final temperature of the blocks needs to be the same, in order to achieve the thermal equilibrium.

Hence, the phenomenon described violates the zeroth law of thermodynamics.

Therefore, option (A) is correct.

Explanation for incorrect options:

First Law of Thermodynamics:

1. The First Law of Thermodynamics states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy.
2. This means that heat energy cannot be created or destroyed, it can, however, be transferred from one location to another and converted to and from other forms of energy.

Second Law of Thermodynamics:

1. The second law clearly explains that it is impossible to convert heat energy to mechanical energy with 100 percent efficiency.
2. For example, if we look at the piston in an engine, the gas is heated to increase its pressure and drive a piston. However, even as the piston moves, there is always some leftover heat in the gas that cannot be used for carrying out any other work. Heat is wasted and it has to de discarded.

Third Law of Thermodynamics:

1. The third law of thermodynamics states that the entropy of a perfect crystal at a temperature of zero Kelvin (absolute zero) is equal to zero.

Therefore, options (B), (C), and (D) are incorrect.

Hence, option (A) is the correct answer.