The question asks about the direct consequence of the Zeroth Law of Thermodynamics. We need to understand what the Zeroth Law states and what fundamental concept it establishes.
Therefore, the Zeroth Law directly leads to the concept of temperature and its measurement.
C) Temperature — The Zeroth Law of Thermodynamics establishes the concept of temperature as a fundamental property that determines thermal equilibrium between systems. It provides the logical basis for the use of thermometers.
The question asks about the spontaneous direction of heat flow. This is a fundamental concept in thermodynamics, specifically related to the second law of thermodynamics. We need to identify the physical property whose difference drives the spontaneous transfer of heat.
D) A body at higher temperature to a body at lower temperature. This statement correctly describes the spontaneous direction of heat flow, which is dictated by the temperature gradient between two bodies.
The question asks for the definition of the internal energy (U) of a system. Internal energy is a fundamental concept in thermodynamics, representing the total energy contained within a thermodynamic system.
Correct Option: A) The sum of kinetic and potential energies of all molecules in the rest frame of the system. This option accurately defines internal energy by including both microscopic kinetic and potential energies and specifying the appropriate reference frame (rest frame of the system).
The internal energy of an ideal gas is a fundamental concept in thermodynamics. Understanding its dependence on state variables like pressure, volume, and temperature is crucial. For an ideal gas, the particles are assumed to have no intermolecular forces and negligible volume. This simplification leads to a direct relationship between internal energy and temperature.
B) Temperature only
The question asks to identify the nature of internal energy in thermodynamics. We need to understand the definitions of state variables and path variables.
D) State variable — depends only on the state, not on the path. This correctly defines a state variable and applies it to internal energy. The internal energy of a system is uniquely determined by its current thermodynamic state (e.g., defined by pressure, temperature, and volume), irrespective of the process or path that led to that state.
To determine which option is NOT a thermodynamic state variable, we need to understand the definition of a state variable (or state function) in thermodynamics. A state variable is a property of a system that depends only on the current state of the system, not on the path taken to reach that state. In other words, its change between two states is independent of the process.
The change in a state variable, say \(X\), between two states 1 and 2 is given by \(\Delta X = X_2 - X_1\), which is independent of the path. For a path function like heat \(Q\), we write \(\delta Q\) (or \(dQ\)) to denote an infinitesimal amount, and its integral \(\int \delta Q\) depends on the path.