Prevost Theory Of Exchange

The concept of thermal equilibrium was applied to radiation by Prevost. The pace at which a body radiates or absorbs heat, according to him, is determined by the nature of its surface, its temperature, and the temperature of its surroundings. As a body’s temperature rises, so does the overall amount of heat it emits. 

He claimed that all bodies emit energy, but that hot bodies emit more than cooler bodies. At a higher temperature, a body radiates more heat energy to the surroundings than it gets from it. That is why, when we stand in front of the furnace, we feel warm. When you touch someone, for example, they may perceive your skin as hot or cold.

Heat Transfer Theory

The driving energy in a system is always allowed to flow until equilibrium is attained by the inherent principles of physics. As long as there is a temperature difference, heat will leave the warmer body or the hottest fluid and be transported to the cold medium.

Several basic rules regulate the theory of heat transmission from one medium to another, or from one fluid to another.

• Heat is always transmitted from a hot source to a cold source.

• A temperature difference between the medium is required at all times.

• Except for losses to the environment, the quantity of heat lost by the hot medium is equal to the amount of heat acquired by the cold medium.

Radiation

Radiation does not require any kind of material medium to transport heat. A body emits energy, which travels through space in the same way as light does. When it collides with a material body, a portion of it is absorbed, and the receiving body’s thermal energy is enhanced. This is how the sun’s heat reaches the planet, after travelling millions of kilometres over empty space.

Prevost Law

Pierre Prévost proposed the notion of radiation in a systematic method in 1792, which is now known as the theory of exchange. All bodies, according to this principle, emit thermal radiation at all temperatures. The amount of thermal radiation radiated per unit time is determined by the nature, area, and temperature of the emitting surface. At greater temperatures, the pace accelerates. Furthermore, when thermal radiation from the surrounding bodies falls on a body, it absorbs a portion of it. A body’s temperature drops when it radiates more energy than it absorbs. The temperature of a body rises when it emits less energy than it absorbs.

Example:

Let’s prove this law by taking an example:

Consider a body that has been held in a room for a long time. The temperature of the body is found to be constant and equal to room temperature. The body continues to emit heat radiation. However, it also absorbs some of the radiation released by nearby objects, walls, and other structures.

Observations

•  When a body’s temperature is equal to that of its surroundings, it radiates at the same rate as it absorbs.

• When we put a hotter body in the room, it radiates at a higher pace than it absorbs heat. As a result, the body loses a net amount of thermal energy over time, and its temperature drops.

• In a similar way, when a colder body is kept in a warm environment, it radiates less energy to the environment than it absorbs. As a result, the total amount of thermal energy in the body increases, and the temperature rises.

Prevost Theory of Exchange formula

As it is only a theory and not a law having mathematical formulae, it has no formula but certain conclusions drawn by the theory can be expressed as,

Q(net) is positive if Q (absorbed) is higher which means heat is gained.

Q(net) is negative if Q (emitted) is greater which states there is a loss of heat.

Example 1:

A body with an initial temperature of and another body with an initial temperature of are placed in an evacuated enclosure with walls kept at 10 degrees Celsius. Give an answer using the Prevost theory of exchange. 

Solution: Both X and Y will get heat radiated by the walls of the enclosure as free radiant heat, according to Prevost, is an extremely rare fluid whose beams, like light rays, travel through each other without causing detectable interference. According to Prevost’s idea of exchanges, each body emits and absorbs radiation from other bodies. Each body emits radiation regardless of the presence or absence of other bodies.

Conclusion

Radiant energy, thermal radiation, or simply radiation is the name given to the energy emitted by a body without any medium. As a result, the term “radiation” has two meanings. It is the process through which energy is emitted by a body, transferred through space, and then absorbed by another body. According to Prevost, all bodies emit energy, but that hot bodies emit more than cooler bodies.