As far as I know from physics lessons I got at school, electrons go up to higher energy levels when they capture a photon. But, once an electron is at a given level, what makes it go down to a lower level and emit a photon? Is there a constant time during which an electron is able to stick at a level, and then jump to a lower level? I mean, I know electrons tend to reach low energy levels, but can you describe this process? Put in other words, how does an electron "know" there are lower energy levels and when does an electron choose to lose energy?

# [Physics] What makes electrons lose energy

electrons

#### Related Solutions

I want to ask how electrons travel though the different orbitals?

Electrons are quantum mechanical entities,they cannot be described by the motions of classical billiard balls. That is why the terminology "orbital" was invented. We only know about the electron around the proton in the hydrogen atom that when probed, it has a probability of being within the orbital solution.

As far as the mathematics goes there is only the probability and no continuity between two space points so that a classical velocity could be defined.

They can only have discrete amount of energies (energy levels). If it doesn't have enough energy to go to higher energy level,

The electron remains at its energy level, unless a photon with the appropriate energy hits the atom. Orbitals might mathematically overlap in space, particularly if there are many electrons, this does not mean there is an energy exchange, it just means that the *probabilities* of two energy orbital can overlap in space. Only if there is a probability for an energy transfer to a lower state then the space overlap has a meaning. This is how electron capture happens with nuclei , the S level overlaps with the nucleus and there exists a probability for the electron to be captured by a proton given the energy balances of the system.

it will come back to the lower one. This happens instantaneously.

See above. The electron is not moving like a billiard ball. Its path is not consecutive. There are only probabilities.

There is nothing instantaneous in quantum mechanics . If one wants to go to the details of "electron interacting with a photon" one has to go to quantum field theory, where the interactions are described with Feynman diagrams and there are constants characterizing them which define the order of magnitude of the time transition.

So does it move with infinite velocity within two energy levels during transition?

No , there are no infinities . If the electron is in an energy level that can release a photon and relax to the lower level, there exist time constants coming from the probability distributions which give a lifetime for the decay and a width to the energy line.

If it is at the ground state it will stay in the ground state forever, unless an appropriate energy photon hits the atom, either to kick it up an energy level or free it from the material completely, as in the photoelectric effect.

Take a look at the Drude model. It gives a fairly intuitive way to look at conductivity in solids. Although later proved to be slightly incorrect due to the ignorance of quantum effects, it does the job for a classical explanation.

One can reason as to how heat is generated in the conducter in a classical manner from the Drude model. As the electrons move through the conducter, a few electrons strike the constituent atoms or molecules. Since the atoms/molecules acquire kinetic energy, the temperature of the conducter as a whole increases. Any object having surface area $A$ with temperature $T$ emits electromagnetic radiation with power $$P=A \epsilon \sigma T^4$$ according to the Stefan-Boltzmann law, where $\epsilon$ and $\sigma$ are constants.

## Best Answer

The electron itself doesn't "know". The entire system "knows" what its own energy levels are. That is, the system can make transitions only to states that exist. Don't think of the electron, think of the entire system that contains the electron.

The system will stay at the excited level for some period of time depending on the strength of the coupling between the system and the electromagnetic field, and the intensity of the field. Stronger coupling means shorter lifetime. And stronger field means shorter lifetime. This last effect is

stimulated emission.There is never a situation where the field has no intensity. The ground state of the electromagnetic field has "zero-point fluctuations", required by the uncertainty principle. No energy can be extracted from the field in the ground state, so it behaves like zero intensity. But the zero-point field can induce transitions in an atom just as in stimulated emission. This is the origin of

spontaneous emission, the process by which an isolated excited system makes transitions to lower energy states.