Final answer:
A perfectly opaque object that absorbs and reemits all radiation as thermal radiation is known as a blackbody, which is the most effective at both absorbing and emitting radiation. It is characterized by an emissivity of 1, indicating perfect absorption and emission across all wavelengths, contrasting with white or transparent objects which reflect or transmit radiation.
Step-by-step explanation:
A perfectly opaque object that absorbs all radiation and reemits the absorbed energy as thermal radiation is known as a blackbody. This concept is used to describe objects that are ideal absorbers and emitters of electromagnetic radiation. According to the description provided, such an object does not reflect or scatter any radiation but instead absorbs all of it. This characteristic allows astronomers to refer to stars as blackbodies even though they shine brightly in a variety of colors. The phenomenon of radiation absorption and emission is also influenced by an object's color; black objects are the most effective at both absorbing and radiating energy.
For instance, black asphalt is hotter than a gray sidewalk on a summer day because it absorbs more radiation. Conversely, it will also be colder on a clear summer night since it radiates energy more efficiently than gray. A true blackbody would have an emissivity (e) of 1, indicating that it absorbs and emits radiation perfectly across all wavelengths of the electromagnetic spectrum, unlike white objects that reflect most of the radiation and transparent objects that allow radiation to pass through without absorption.