Thermal radiation is emitted when particles vibrate or are heated up due to the fundamental nature of the thermal energy carried by the particles. This emission is a result of the thermal motion of charged particles, such as electrons and atoms, within the material.
When particles are heated or gain energy, their thermal motion becomes more intense. They vibrate, rotate, and move more vigorously. This increased thermal energy causes the charged particles to undergo acceleration and deceleration, resulting in the emission of electromagnetic waves.
According to classical electromagnetism, accelerating charges emit electromagnetic radiation. In the case of thermal radiation, the accelerated charges are the charged particles within the material undergoing thermal motion. As they oscillate and vibrate, they create changing electric fields and varying current densities, which in turn generate electromagnetic waves.
The emitted thermal radiation spans a wide range of frequencies, forming a continuous spectrum known as a black body spectrum. The specific frequencies emitted depend on the temperature of the material. Higher temperatures correspond to more energetic vibrations and greater emission of higher-frequency radiation, including visible light, while lower temperatures result in predominantly lower-frequency radiation, such as infrared.
Overall, the emission of thermal radiation is a natural consequence of the thermal energy possessed by particles and the interaction of their charged components with electromagnetic fields.