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What is Light Emission Light can be produced by matter which is in an excited state and, as we will show, excitation can come from a variety of sources. Black body radiation A body at a given temperature also emits a characteristic spectrum of light called black body radiation.
Name Excitation source Examples of use Chemiluminescence Chemical reactions Emergency lighting Cathodeluminescence Electron beam Electron beam Sonoluminescence Sound energy Possible chemical reactions Triboluminescence Friction energy Gives rise to light emission seen when opening gum labels in the dark.
You have successfully logged out. The energy of an electron in an atom is negative. The negative sign indicates that we need to give the electron energy to move it from the hydrogen atom.
Giving the electron energy will increase the amound of energy in the atom. The electron stays in an excited state for a short time. When the electron transits from an excited state to its lower energy state, it will gice off the same amound of energy needed to raise to that level. This emitted energy is a photon. The energy of the photon will determine the color of the Hydrogen Spectra seen. This, in essence, is the photoelectric effect.
The photons of a beam of light have a characteristic energy proportional to the frequency of the light. In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function of the material the electron binding energy , it is ejected.
If the photon energy is too low, the electron is unable to escape the material. Increasing the intensity of the light increases the number of photons in the beam of light and thus increases the number of electrons excited but does not increase the energy that each electron possesses.
The energy of the emitted electrons does not depend on the intensity of the incoming light the number of photons , only on the energy or frequency of the individual photons. It is strictly an interaction between the incident photon and the outermost electron. Electrons can absorb energy from photons when irradiated, but they usually follow an all-or-nothing principle.
Typically, one photon is either energetic enough to cause emission of an electron or the energy is lost as the atom returns back to the ground state. For a given metal, there exists a certain minimum frequency of incident radiation below which no photoelectrons are emitted. This frequency is called the threshold frequency. Increasing the frequency of the incident beam and keeping the number of incident photons fixed resulting in a proportionate increase in energy increases the maximum kinetic energy of the photoelectrons emitted.
The number of electrons emitted also changes because the probability that each impacting photon results in an emitted electron is a function of the photon energy.
However, if just the intensity of the incident radiation is increased, there is no effect on the kinetic energies of the photoelectrons.
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