Understanding the Zeroth Law of Thermodynamics

The question asks who coined the term 'zeroth law of thermodynamics' and describes the law's core principle: two bodies in equilibrium with a third are in equilibrium with each other. This law is fundamental to the concept of temperature.

Let's look at the options provided, who are all prominent figures in physics and thermodynamics:

• James Clerk Maxwell: Known for his equations of electromagnetism and contributions to the kinetic theory of gases.
• Josiah Willard Gibbs: A founder of chemical thermodynamics, known for concepts like Gibbs free energy.
• Max Planck: Considered the founder of quantum theory, also made significant contributions to thermodynamics, particularly regarding blackbody radiation.
• Ralph H Fowler: An English physicist known for his work in thermodynamics and statistical mechanics.

While the principle described by the Zeroth Law was understood before, it was not formally recognized as a law until later. It was Ralph H Fowler who explicitly formulated this statement and named it the "Zeroth Law" because its importance in defining temperature makes it logically precede the First and Second Laws of Thermodynamics, even though it was stated later chronologically.

The Zeroth Law can be stated as:

If body A is in thermal equilibrium with body C, and body B is also in thermal equilibrium with body C, then body A is in thermal equilibrium with body B.

This allows us to define temperature: objects in thermal equilibrium with each other have the same temperature.

Analysis of the Options and the Correct Answer

Based on the history of thermodynamics, the physicist credited with coining the term 'zeroth law of thermodynamics' is Ralph H Fowler.

The law was proposed in 1931, after the First and Second Laws had already been established, but its foundational nature led Fowler to number it "zero".

Let's confirm why the other options are incorrect:

• James Clerk Maxwell contributed significantly to thermal physics but is not credited with coining the Zeroth Law.
• Josiah Willard Gibbs developed much of the theoretical framework for chemical thermodynamics but did not coin the Zeroth Law.
• Max Planck's work in thermodynamics was crucial, especially concerning entropy and energy quanta, but he is not associated with naming the Zeroth Law.
• Ralph H Fowler, working with Edward A. Guggenheim, formalized this principle and gave it its now-famous name.

Therefore, the correct answer is Ralph H Fowler.

Revision Table: Key Thermodynamic Laws

Additional Information on the Zeroth Law and Temperature

The Zeroth Law of Thermodynamics is crucial because it provides the basis for the concept of temperature and the use of thermometers. A thermometer works by coming into thermal equilibrium with the object whose temperature is being measured. If two objects register the same temperature on the same thermometer, the Zeroth Law tells us they are in thermal equilibrium with each other, meaning they have the same temperature.

Before the Zeroth Law was formally stated, the concept of thermal equilibrium was used, but defining temperature rigorously proved challenging. The Zeroth Law provides that rigorous foundation.

The principle of the Zeroth Law is intuitively understood from everyday experience. For example, if a cup of hot tea is placed in a room, it eventually cools down to the room's temperature (thermal equilibrium with the room). If another object, like a book, is also in the same room for a long time, it is also at room temperature. If the tea and the book are then brought into contact (assuming no heat transfer with the surroundings), no further change in temperature occurs between them because they were already in thermal equilibrium with the room, and thus with each other, according to the Zeroth Law.