Stefan’s law

An Austrian physicist named Sir Josef Stefan proposed Stefan’s Law in 1879 after conducting some practical experiments. The same concept was deduced from thermodynamics in 1884 by Austrian scientist Ludwig Boltzmann. 

Radiation is the net energy that takes birth from a source and navigates at the speed of light by a medium called space. This energy is linked to an electric field and a magnetic field, and it exhibits attributes that are similar to waves. Radiation can also be referred to as “electromagnetic waves”. 

What is radiation?

Radiation is the flow of energy. Electromagnetic radiation (EMR) is the term used to describe the energy that moves in waves. Another approach to consider EMR is a matterless bundle of energy known as a photon. The photon is a bundle of energy that transfers energy through space. On the other hand, particulate radiation is made up of tiny particles (electrons, alpha particles) that transport energy. Particulate radiation can be emitted by radioactive materials as well as linear accelerators. Due to the poor penetration of matter, particle radiation is ineffective for imaging.

Heat or thermal radiation

Thermal radiation in Physics is defined as the transfer of energy due to the emissions of electromagnetic waves that carry with them some amount of energy far from the emitting object. At an ordinary temperature, the radiation takes place in the infrared region of the electromagnetic spectrum. The relationship that looks after the total radiation from a hot object is called Stefan-Boltzmann’s law.

What is blackbody and blackbody radiation?

A blackbody in physics is related to an opaque object and an object that gives out thermal radiation. An ideal blackbody is an object/ body that absorbs all incoming light and fails to reflect any. When a specific given object appears to be black at normal room temperature, then that body is black. But in any case, if the body is exposed to a high temperature, then a blackbody will start to glow due to thermal radiation.

Every object gives out thermal radiation (making sure that its temperature is more than the Absolute Zero, or -273.15 degrees Celsius). Still, every object fails to give out thermal radiation in a perfect manner. Instead, they prove to be much better at absorbing and emitting some light wavelengths than others. These efficiencies that are not consistent throughout make it difficult to analyse the interaction of heat, light, and matter using general objects/ bodies.

How can one make a blackbody?

With help and knowledge, it is very well possible to build/ create a close to perfect blackbody. To do this, one must make a conductive and thermal material box, for example, metal. Then the box must completely be closed from all its sides, as a result of which the inner part of the box forms a hollow cavity that receives zero or no amount of light from the surrounding areas. After this, one must drill a tiny hole anywhere on the surface of the metallic box. The light that comes out/ passes through this hole will be nearly perfect and thus demonstrate the light from a perfect blackbody for the temperature of the air present inside the box.

What is Stefan’s law or Stefan-Boltzmann’s law in physics?

The amount of total radiant heat energy emitted from a surface is proportional to the fourth power of its absolute temperature. This is proposed by Stefan’s Law in the field of Physics.

In simple words, Stefan’s law Definition or Stefan-Boltzmann law states that the amount of total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.

Suppose ‘E’ denotes the radiant heat energy emitted from a surface of the unit area in time one second (power/ unit area) and ‘T’ indicates the absolute temperature (measured value in Kelvin). In that case, E = σT4, Sigma ‘σ’ represents the constant of proportionality called the Stefan-Boltzmann constant in Physics. 

Stefan-Boltzmann’s constant in Physics is around  5.670374419 × 10−8 watt per metre2 per Kelvin4.  

The Stefan-Boltzmann law is only applicable to black bodies, which means a body whose surface can absorb all the incident heat radiations.

Definition of Stefan’s law in Physics

Stefan’s law or Stefan-Boltzmann law states that the amount of total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature.

Formula stating this law is E = σT4

In the above-given formula,

E = radiant heat energy emitted from a surface of the unit area in time one second.

σ = Stefan-Boltzmann constant.

T = Absolute temperature.

On the basis of the surface temperature of the Sun’s photosphere (6000 K), and the Stephan-Boltzmann law, the net energy that is emitted by the Sun is

Esun = ∊ σ T4 

       = 1 x 5.67 x 10-8 x 60004 

       = 25.12 x 109J m-2 s-1    (approximate value)

Conclusion

Radiation comes in different forms of energy in motion. This article tells us that the amount of radiation emitted by a surface at a particular wavelength is determined by the material of the body, the state of the surface, and the temperature. As a result, various materials release varying quantities of radiation energy. A blackbody is a body that absorbs all of the radiation that falls on it while producing massive amounts of heat at its absolute temperature.