Final answer:
When an electron drops from a higher to a lower energy level in an atom, it emits a photon containing the energy equivalent to the difference between the two levels, aligned with the conservation of energy law.
Step-by-step explanation:
When an electron changes from a higher energy state to a lower energy state within an atom, a quantum of energy is emitted as a photon. This principle is based on the Bohr model of the atom, where electrons orbit the nucleus at certain energy levels. When an atom is in its ground state, the electrons are at the lowest energy level possible. If the atom absorbs energy, electrons can jump to a higher energy level, called an excited state. The energy levels are quantized, meaning electrons can only exist at specific energy levels, not in between.
According to the law of conservation of energy, the energy absorbed by an electron to move to a higher energy state is equal to the energy emitted as a photon when the electron falls back to its lower energy state. The emitted photon has a specific energy, which corresponds to the difference in energy between the two levels, and this energy is expressed as E = hf, where 'h' is Planck's constant and 'f' is the frequency of the emitted photon.