PHOTOELECTRIC EFFECT

The photoelectric effect is the expenditure of electrons from a surface (usuallymetal) when charged, and absorb, electromagnetic radiation (such as visible light and ultraviolet radiation) that is above the threshold frequency depends on the type of surface. Before you continue reading, help us to click the image on the side. An old term for the photoelectric effect is the effect of Hertz (which is currently not used anymore). Hertz observe and then indicates that theelectrode is illuminated with ultraviolet light creates sparks of electricity more easily.

Photoelectric effect requires photons with energy of a few electronvolts to over1 MeV high atomic number elements. Study of the photoelectric effect led toimportant steps in understanding the quantum nature of light, the electrons andaffect the formation of wave-particle Duality concept. the phenomenon in whichthe light affects the motion of electric charges include the effects offotokonduktif (also known as fotokonduktivitas or photoresistivity), thephotovoltaic effect, and fotoelektrokimia effects.

History

In 1899, J. J. Thomson investigated ultraviolet light in CRT. Influenced by thework of James Clerk Maxwell, Thomson deduced that cathode rays consisted ofnegatively charged particles, which he called corpuscles (later to be called"electrons"). In such research, Thomson put the metal plate (cathode) in thevacuum tube, and exposed it with high-frequency radiation.

Photoelectric Effect

When a beam of light on metal, there are electrons out of the metal surface. The symptoms of this so-called photoelectric effect. The photoelectric effect is observed through the following procedures. Two pieces of sheet metal (thin metal plate) separated placed inside the vacuum chamber. Beyond the secondthese plates tubes connected to each other with wire. Firstly there is no current flow because the two plates apart. When light of the appropriate subject to one of the plates, the electric current is detected on the wire. This happens due tothe electrons off of one of the plates and headed to the other plates togetherform an electric current.

The results of observation of the symptoms of the photoelectric effect conjures up a number of facts which are characteristic of the photoelectric effect.Characteristics that are as follows.

only the appropriate light (which have a greater frequency of certain frequenciesonly) that allows the release of electrons from the metal plate or cause the photoelectric effect occurs (marked with detection of electric current on a wire).A specific frequency of light where the electron is detached from the metal surface is called the frequency threshold in metals. This frequency is different for each metal and metal is characteristic of it.

When the light used can produce photoelectric effect, increased the intensity of light coupled with the increase of the number of electrons that are detached from the metal plate (marked with an electric current that gets larger). However,the photoelectric effect does not occur for light with a frequency that is less than the threshold frequency despite the intensity of the light is enlarged.

photoelectric effect, occurs when an electric current is detected on the series the wire as soon as the appropriate light is illuminated on a metal plate. This meansalmost no interval of electrons free from the surface of the metal after the metalglowing light.

Characteristics of the photoelectric effect cannot be explained using the wave theory of light. Required new viewpoints in describing the light where light is not viewed as a wave of energy that can have continuous but rather light asparticles.

Device theory that describes light as a wave is not available through the concept of discrete or quantized energy developed by Planck and proven according to explain heat radiation spectrum of black body. The concept of quantized energywas used by Einstein to explain the occurrence of the photoelectric effect. Here, the light is seen as a quantum of energy that only have discrete energy isn'tcontinuous expressed as

E = hf.

Important concept that Einstein put forth as the background of the occurrence of the photoelectric effect is that one electron absorbs a quantum of energy.One quantum of energy is absorbed by the electrons used to be separated fromthe metal and to move to the metal plate to the other. This can be written as

Light energy = Energy + Kinetic Energy threshold electrons maximum

E = Wo + Ekm

HF = hfo + Ekm

EKM = hf – hfo

This equation is called the Einstein equations for the photoelectric effect. Note that Wo is the energy threshold of metal or metal work function, fo is the frequency threshold in metals, f is the frequency of light used, and Ekm ismaximum kinetic energy the electrons off of the metal and move to the metal plate to the other. In other forms of equations for the photoelectric effect can be written as

Where m is the mass of an electron and an electron's speed and is ve. The SIunit of energy is the joule (J) and frequency is hertz (Hz). However, the work function of the metal is usually expressed in units of the electron volt (eV) so keep in mind that 1 eV = 1.6 × 10 ^ − 7 J.

Emission Mechanisms

Photons have an energy beam from the characteristics determined by the frequency of the light. In photoemission process, if the electrons in some materials absorb the energy of one photon and thus have more energy than thework function (the electron binding energy) of the material, was issued. If the photon energy is too low, can't get it out of the material. An increase in the intensity of the rays increased the number of photons in a beam of light, and thus increase the number of electrons, but does not increase energy perelectron dimemiliki. The energy of the emitted electrons does not depend onthe intensity of the incoming light, but only on the energy or frequency ofindividual photons. It is the interaction between photons and electrons of the outermost.

Electrons can absorb energy from photons when irradiated, but they usuallyfollow the principle "all or nothing". All the energy of a photon must beabsorbed and used to liberate an electron from an atom that binds, or energy is emitted again. If the photon energy is absorbed, most liberating energy of electrons of atoms, and the rest of dikontribusi to the kinetic energy of the electron as a particle free.

There are no electrons released by radiation below the frequency threshold, because the electrons are not getting enough energy to overcome the bonding of atoms. The emitted electrons usually called fotoelektron in many textbooks.

The photoelectric effect helped wave-particle duality, where physical systems(such as the photon in this case) can indicate both the nature and behaviour ofthe wave-like and particle-like, a concept that is widely used by the creator ofquantum mechanics. The photoelectric effect is described mathematically by Albert Einstein that expand quanta, developed by Max Planck.

The law of the photoelectric emission:

For metals and certain amount of fotoelektro radiation emitted is directly proportional to the intensity of light used.

For certain metals, there is a minimum frequency of radiation. below this frequency fotoelektron can not be emitted.

Above these frequencies, the kinetic energy of the emitted fotoelektron do not depend on the intensity of the light, but depends on the frequency of the light.

Time difference from radiation and emission of fotoelektron is very small, less than 10−9 seconds.

Potential Penghenti

The relationship between current and voltage applied to describe the nature ofthe photoelectric effect. For the discussion, the light source illuminating the Pplate, and another electrode plate Q collect any electrons emitted. We vary the potential between P and Q, and measure the current flow in the external circuitbetween the two plates.

If the frequency and the intensity of the incident radiation is fixed, the photoelectric current is increased incrementally with increasing positivepotential until all electrons emitted are collected. The photoelectric current isreaching the saturation value and did not improve further to increase the positive potential. Saturation currents depends on the intensity of the lighting,but not wavelength.

If we apply the potential negative to plate Q with respect to plate P and gradually increase it, is reduced when the photoelectric until zero, on certainnegative potential at the plate a minimum of negative potential of q. given to the plate where the photoelectric current Q to zero is called a potential stoppingor cutting potential. [7]

For a given frequency of radiation incidents, potential stops is independent of the intensitasnya.

For a given frequency of radiation incidents, potential Vo to stop dealing withthe maximum kinetic energy of fotoelektron that just stopped from t. platereaches if m is the mass and v is the speed Max maximum fotoelektron emitted, then:

Kmax = 1/2 m v ^ 2

If e is the charge on the electron and V 0 is retaining potential, then the work performed by the potential slowdown in stopping the electron e = V 0, which provides:

1/2 m v ^ 2 = e. Vo

The relationship above shows that the maximum speed of fotoelektron emitteddoes not depend on the intensity of the incident light. Therefore,

Kmax = e. Vo

Stop voltage varies linearly with the frequency of the light, but it depends on the type of material. For certain material, there is a frequency threshold that must bereached, is independent of the intensity of the light, to observe the emission of electrons.

A Three-Step Model
In the x-ray regime, the photoelectric efect in crystalline material is oftendecomposed into three steps:

1. Inner photoelectric effect (see diode below). The hole left behind can cause the auger effect, which is visible even when the electrons leave no material. Inmolecular solids phonons are excited in this step and can be seen as the line inthe final electron energy. The inner photoeffect has to be dipole allowed. Theinner photoeffect has to be dipole allowed. The transition rules for atomstranslate via the tight-binding model onto the Crystal. They are a similargeometry to plasma oscillations in that they must be transversal.
2. Ballistic transport is half of the electrons to the surface. Some electrons arescattered. Some of the electrons are scattered.
3. Electrons escape from material on the surface.

In a three-step model, electrons can take multiple paths through three steps. Allthe roads can be annoying in the sense of an integral path formulation. For the State of the surface and the molecule is a three-step model does it still make sense even some as the most atoms have electrons that can spread someelectrons leave.

Reference:
https://id.wikipedia.org/wiki/Efek_fotolistrik
https://aktifisika.wordpress.com/2010/02/22/sifat-particles of light-photoelectric-effect-/

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Ditulis mukri — Thursday 18 February 2016 — Add Comment — Modern Physics