In thermodynamics, the spontaneous flow of thermal energy from a hotter body to a colder body is called what?

Introduction / Context:

In everyday language people often confuse the words heat and temperature, but in physics they have precise meanings. This question aims to clarify that distinction by asking what we call the flow of thermal energy from a region of higher temperature to a region of lower temperature.

Given Data / Assumptions:

• There are two bodies or regions at different temperatures.
• Thermal energy moves from the hotter body to the colder body.
• We are concerned with the energy in transit, not the energy stored.

Concept / Approach:

Heat in physics is defined as the energy that is transferred between systems or bodies due to a temperature difference. It flows spontaneously from higher temperature to lower temperature until thermal equilibrium is reached. Temperature, on the other hand, is a measure of the average kinetic energy of the particles in a body. Electric current, voltage, and potential difference are electrical concepts and do not describe thermal energy flow directly. Therefore, the correct term for the flow of thermal energy is heat.

Step-by-Step Solution:

Verification / Alternative check:

In thermodynamics, when we write the first law of thermodynamics, we use Q to denote heat added to a system, where Q represents energy transferred. Temperature is represented by T and does not itself represent an amount of energy transferred. This supports the idea that heat is the correct term for the energy flow.

Why Other Options Are Wrong:

Option B: Electric current is the rate of flow of electric charge in a conductor, measured in ampere.

Option C: Voltage is another name for electric potential difference and relates to electric circuits.

Option D: Potential difference is an electrical term and not used to describe thermal energy transfer between bodies.

Common Pitfalls:

Students sometimes say that a body contains heat, but strictly speaking a body contains internal energy and heat is the energy that flows between bodies. Remember that heat flows from hot to cold until temperatures become equal, and it is this flow that the term heat refers to.

Final Answer:

The flow of thermal energy from a hotter body to a colder body is called heat.