The physical meaning is that in general, part of the heat added to the working medium is consumed as expansion work, and the other part is stored in the working medium, which increases the internal energy of the working medium. Heat can be converted into work, and work can also be converted into heat. When a certain amount of heat disappears, it will produce a certain amount of work. When a certain amount of work is consumed, a certain amount of heat will be generated.

The first law of thermodynamics is the law of energy transformation and conservation. In the process of thermal phenomena, internal energy and other forms of energy are transformed into each other.

Matters needing attention in the formula of the first law of thermodynamics;

The first law of thermodynamics is essentially equivalent to the law of conservation of energy, and it is a universal law, which is applicable to all systems in the macro world and the micro world and to all forms of energy.

Since 1850, the scientific community has realized that the law of conservation of energy is one of the universal laws of nature.

The law of conservation and transformation of energy can be expressed as:

All substances in nature have energy, and energy has various forms, which can be transformed from one form to another, but in the process of transformation, the total value of energy remains unchanged.

The first law of thermodynamics is a special form of the law of energy conservation and transformation in the field of thermal phenomena. It is a summary of human experience and one of the most basic laws of thermodynamics.