Final answer:
Thermal radiation is the transmission of heat via electromagnetic waves between objects of different temperatures, largely in the infrared spectrum, and can be felt as warmth. The power of radiation depends on the object's temperature, following the Stefan-Boltzmann law.
Step-by-step explanation:
Thermal radiation is defined as the transfer of heat through the emission or absorption of electromagnetic waves. This process occurs between any two objects when their temperatures differ, with heat typically moving from the hotter to the cooler body. One of the most familiar examples of thermal radiation is the warmth felt from the sun on a clear day, but it also includes the heat lost from the human body into the surrounding environment. The energy associated with thermal radiation depends on the temperature of the emitting object and is governed by the Stefan-Boltzmann law, which states that the power radiated increases with the fourth power of the absolute temperature of the object. The majority of thermal radiation that is felt as heat by humans is in the infrared spectrum. Additionally, when an object is sufficiently hot it can emit visible light, such as the red glow of an electric stove element or the white of molten steel in a furnace, indicating the object's temperature. Therefore, the most accurate definition of thermal radiation in the provided options would be: 1) radiation that depends only on the emitting object's temperature, and to a lesser extent 4) radiation produced by a hot object.