In the Bohr model of the atom, electrons occupy specific quantized energy levels or orbits around the nucleus. According to classical electromagnetism, an accelerated charged particle, such as an electron moving in a circular orbit, will emit electromagnetic radiation.
When an electron is in a higher energy orbit, it is in an excited state. To transition to a lower energy orbit, the electron must release energy. This energy release occurs in the form of electromagnetic radiation, often in the form of photons.
The emission of electromagnetic radiation happens because the electron's energy must be conserved. As the electron moves from a higher energy level to a lower energy level, it releases the excess energy in the form of a photon. The energy of the photon is directly related to the energy difference between the initial and final orbits. According to the Planck-Einstein relation, the energy of a photon is given by E = hf, where E is the energy, h is Planck's constant, and f is the frequency of the radiation.
This phenomenon is known as spontaneous emission. The emitted electromagnetic radiation can be in the form of visible light, ultraviolet light, or even X-rays, depending on the energy difference between the electron orbits. The emission spectrum of an atom, consisting of specific wavelengths or frequencies of light, is a result of these transitions between different energy levels.
It is worth noting that the Bohr model is a simplified representation of atomic structure, and a more accurate understanding of electron behavior requires quantum mechanics. In quantum mechanics, the concept of electron orbitals is used to describe the probability distribution of finding an electron in a particular region around the nucleus. The emission of electromagnetic radiation is still explained by transitions between energy levels, but the detailed behavior of electrons is described by wave functions and probability amplitudes rather than classical orbits.