Photoelectric effect

The photoelectric effect is the emission of electrons from a usually metallic surface upon exposure to, and absorption of, electromagnetic radiation, such as visible light or ultraviolet radiation. An older term for the photoelectric effect was the Hertz effect, though this phrase has fallen out of current use.http://scienceworld.wolfram.com/physics/HertzEffect.html

Explanation

The photons of the light beam have a characteristic energy given by the wavelength of the light. In the photoemission process, if an electron absorbs the energy of one photon and has more energy than the work function, it is ejected from the material. If the photon energy is too low, however, the electron is unable to escape the surface of the material. Increasing the intensity of the light beam does not change the energy of the constituent photons, only their number, and thus the energy of the emitted electrons does not depend on the intensity of the incoming light.

Related Topics:
Photoemission - Work function

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Electrons can absorb energy from photons when irradiated, but they follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or the energy is re-emitted. If the photon is absorbed, some of the energy is used to liberate it from the atom, and the rest contributes to the electron's kinetic (moving) energy as a free particle.

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Equations

In analysing the photoelectric effect quantitatively using Einstein's method, the following equivalent equations are used:

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Energy of photon = Energy needed to remove an electron + Kinetic energy of the emitted electron

Related Topics:
Photon - Electron - Kinetic energy

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Algebraically:

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:hf = hf_0 + {1 over 2}{m}{v_m}^2

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Using physicists' symbols:

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:hf = phi + E_k,

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where

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• h is Planck's constant;
• f is the frequency of the incident photon;
• f₀ is the threshold frequency for the photoelectric effect to occur;
• $phi$ is the work function, or minimum energy required to remove an electron from atomic binding, and
• $E\_k$ is the maximum kinetic energy observed.

Note: If the photon's energy (hf) is not greater than the work function (phi), no electron will be emitted. The work function is sometimes denoted W.

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When this equation is not observed to be true (that is, the electron is not emitted or it has less than the expected kinetic energy), it may be because when given an excess amount of energy to the body, some energy is absorbed as heat or emitted as radiation, as no system is perfectly efficient.

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