Final answer:
Photons are emitted when an electron transitions from a higher energy level, or excited state, to a lower energy level, typically the ground state. This process involves releasing energy that was previously absorbed by the electron, and is maintained by the law of conservation of energy.
Step-by-step explanation:
Photons are emitted when a bound electron jumps down to a lower energy state. Essentially, this transition occurs when the electron moves from an excited state, which is a state of higher energy, to a state of lower energy, which is usually the ground state. The energy difference between these two states is released in the form of a photon, a quantum of electromagnetic radiation.
Ground state refers to the lowest energy level an electron can occupy in an atom, whereas an excited state is characteristic of an electron that has absorbed energy and has moved to a higher energy level. The transition of an electron to a lower energy state and the emission of a photon is governed by the principle of conservation of energy. Therefore, the energy contained within the emitted photon is equivalent to the energy difference between the initial and final energy states of the electron.
Atoms generally seek to rest in the ground state, so an electron in an excited state will eventually return to the ground state, usually within a very short timeframe. The emitted photons can carry various amounts of energy, but typically, only a very small number of photons are emitted in such transitions.