Why is light emitted from atoms

Stimulated emission occurs when matter in an excited state is perturbed by a photon of light and gives rise to a further photon of light, typically at the same energy and phase as the perturbing photon. This phenomenon is the process which gives rise to laser emission where you have many photons at the same wavelength and in phase with each other. A body at a given temperature also emits a characteristic spectrum of light called black body radiation.

Consider an electric filament as current is applied to it. As the electric current supplies energy to the filament and it heats up, it starts to glow red, and as it gets hotter it then turns orange and then white. Our filament will approximate a black body and as the filament gains energy from the electrical power it tries to equalize its energy with its surroundings by radiating its excess energy.

It does this by emitting light starting first in the infrared and as the filament gets hotter or has more energy the radiation moves more into the visible spectrum. The spectral irradiance for artificial sources in general deviate from a perfect black body radiation, but the approximation is useful in many applications and by measuring the spectral output of a heated body, its temperature can be remotely measured.

For example, Sunlight is due to the black body radiation characteristic of a body at approximately 5,K see graph below :.

It was discovered later that this didn't happen because electrons can only occupy discrete energy levels within the atom. When an electron drops from a higher energy level to a lower one, the excess energy is emitted as a photon of light. The wavelength, lamda of the photon is inversely proportional to the change in electron energy:. Only certain energy levels are allowed, so only certain transitions are possible and hence specific wavelengths are emitted when an electron drops to a lower energy level.

Conversely, an atomic electron can be promoted to a higher energy level when it absorbs a photon. Again because only certain transitions are allowed, only certain wavelengths can be absorbed. Why do atoms emit or absorb light of specific wavelengths? The emission spectra Ask Question. Asked 2 years, 8 months ago. Active 8 months ago. Viewed 9k times.

Improve this question. Indeed, comparing the similarities of atoms was how the table was designed originally. Also, there needs to be certain attention to detail - e.

Add a comment. Active Oldest Votes. As an example, this is what the spectrum for hydrogen looks like, which is broken up into a number of different spectral series : Image source Generally speaking, the emission spectra of most atoms cover roughly similar wavelength ranges, basically spreading over the visible range with substantial bleed over into the UV and infrared regions.

But you can still ask a very similar question, by inserting an appropriate plural: what determines the colours of light emitted? Improve this answer. Emilio Pisanty Emilio Pisanty k 28 28 gold badges silver badges bronze badges. To summarize: Each atom has many orbitals that its electrons can occupy, and the energies of these orbitals vary from atom to atom.

You cleared up a lot! I was just wondering, can a single electron emit more than one photon in a single 'jump'? Or does it gain and lose energy multiple times and emit a single photon every time? However, it is possible for two photons to be emitted during a single transition, although the frequency of such "two-photon" events is some k times lower than the "single-photon" case: en.

Michael Seifert 32k 3 3 gold badges 65 65 silver badges bronze badges. Karthik Karthik 1, 10 10 silver badges 17 17 bronze badges. For example, you won't find a hydrogen emitting light halfway between the Lyman-alpha and Lyman-beta wavelengths I've performed a slight edit to avoid this confusion, but feel free to roll it back if it conflicts with your intent. Sign up or log in Sign up using Google.

Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Electrons only exist in shells, the area around a nucleus. Specific energy levels correspond to specific shells.

In an atom, the amount of energy levels that are allowed depend on the structure of protons and electrons. Emission is the process of elements releasing different photons of color as their atoms return to their lower energy levels. Atoms emit light when they are heated or excited at high energy levels. The color of light that is emitted by an atom depends on how much energy the electron releases as it moves down different energy levels.

When the electrons return to lower energy levels, they release extra energy and that can be in the form of light causing the emission of light. On the other hand, absorbed light is light that isn't seen. Absorption occurs when electrons absorb photons which causes them to gain energy and jump to higher energy levels.

Notice emission in the picture above. It shows the electron moving down energy levels. The color of the light emitted would result from the amount of energy as it moves through shells.