| English | Black body radiation |
|---|---|
| Bahasa Melayu | Sinaran jasad hitam |
| 中文 | 黑体辐射 |
Definition
The electromagnetic radiation emitted by an ideal body that absorbs all radiation falling on it, whose spectrum depends only on its temperature.
In exam terms
Black body radiation is the electromagnetic radiation given out by an ideal black body, an object that absorbs all radiation falling on it and reflects none. The shape of the emitted spectrum depends only on the body's absolute temperature (in kelvin, K), not on its material.
As the temperature rises, the total energy radiated increases and the peak of the spectrum shifts to a shorter wavelength.
Example of correct use: "A heated metal glows red, then orange, then white as its temperature rises, showing how black body radiation peaks at shorter wavelengths when hotter." The Sun is often treated as an approximate black body radiator.
Do not confuse it with…
Do not confuse black body radiation with the photoelectric effect. Both are historical clues that light energy is quantised, but black body radiation is about the spectrum a hot object emits, while the photoelectric effect is about electrons ejected when light hits a metal.
Both were explained by treating energy as coming in packets, E = hf.
In Paper 2, this is asked as state or describe, for example "State what is meant by a black body" or "Describe how the black body spectrum changes as temperature rises." A good answer notes that a perfect black body absorbs and emits all wavelengths, and that the peak wavelength decreases as temperature increases.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)