what is a photoconductivity?
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(m)\n\nPhotoconductivity is the tendency of a substance to conduct electricity to an extent that depends on the intensity of light-radiant energy (usually infrared transmission or visible light) striking the surface of a sample. Most semiconductor materials have this property.\n\nWhen there is no illumination, a photoconductive sample has a conductance that depends on its dimensions, on the specific material(s) from which it is made, and on the temperature. In most cases, the greater the radiant energy of a specific wavelength that strikes the surface, the higher the conductance of the sample becomes, up to a certain maximum. When the maximum conductance is reached for a particular sample, further increases in irradiation produce no change in the conductance.\n\nPhotoconductive materials are used in the manufacture of photoelectric devices. Typical photoconductive substances consist of germanium, gallium, selenium, or silicon with impurities, also known as dopants, added. Other common materials include metal oxides and sulfides
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During photosynthesis, light energy is converted into chemical potential energy.
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colloid = any system involving two phases where one phase is dispersed in another... the dispersed phase is usually less than 1micrometre in particle size....eg....\n\nmayyonaise is an oil/water suspension;  photographic film is a colloidal suspension of silver halide
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Solar cells work on the principle of the photoelectric effect. If you are not familiar with it, the photoelectric effect explains why when light shines on a metal plate, a current is created. It is because photons in the light displace electrons in the metal. When the electrons are displaced their movement creates a current. It is this effect that allows solar cells to generate electricity:)
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superconductivity is a phenomenopn occuring in certain materials at low temperatures, characterised exactly be zero resistance and the exclusion of the interior magnetic  field.\nTin aluminium, alloys, heavily doped semicoductors etc, show this.
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Unlike traditional cameras that use film to capture and store an image, digital cameras use a solid-state device called an image sensor. These fingernail-sized silicon chips contain millions of photosensitive diodes called photosites. In the brief flickering instant that the shutter is open, each  photosite records the intensity or brightness of the light that falls on it by accumulating a charge; the more light, the higher the charge. The brightness recorded by each photosite is then stored  as a set of numbers that can then be used to set the color and brightness of dots on the screen or ink on the printed page to reconstruct the image. In this chapter, we’ll look closely at this process because it’s the foundation of everything that follows.
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Some molecules absorb visible light, e.g. due to conjugation and pi to pi antibonding transitions, with the highest intensity at a particular wavelength.  One can prepare standard solutions, with accurately devised known concentrations, the measured intensities of these solutions are correlated with these standard solutions, covering a particular dynamic range.  Assuming Beer's Law, the plot will resemble a linear curve, and a least fit regression line and its equation can be obtained; also by correcting for the blank if this is has not bee accounted for by the spectrometer.  The unknown pure solution, or a matrix derived alternative method if the solution is not pure that there are significant impurities in the unknown solution, will also be measured at this wavelength and it's intensity, often the y value, will be plugged into the regression equation to estimate the concentration.
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Early observations\nIn 1839, Alexandre Edmond Becquerel observed the photoelectric effect via an electrode in a conductive solution exposed to light. In 1873, Willoughby Smith found that selenium is photoconductive.\n\n[edit]\nHertz's spark gaps\nHeinrich Hertz, in 1887, made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves, published in the journal Annalen der Physik. His receiver consisted of a coil with a spark gap, whereupon a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box in order to see the spark better; he observed, however, that the maximum spark length was reduced when in the box. A glass panel placed between the source of EM waves and the receiver absorbed ultraviolet radiation that assisted the electrons in jumping across the gap. When removed, the spark length would increase. He observed no decrease in spark length when he substituted quartz for glass, as quartz does not absorb UV radiation.\n\nHertz concluded his months of investigation and reported the results obtained. He did not further pursue investigation of this effect, nor did he make any attempt at explaining how the observed phenomenon was brought about.
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L.E.D. are light emitting diodes, which are comprised of p-n junctions.  P-N junctions are formed using semiconductive material.  P-type semiconductors are composed of positive ions (i.e. holes) and N-type semiconductors are composed of negative ions (i.e. electrons).  When a voltage is added, a current is established, flowing from P to N material.  Current flows only one way through an L.E.D.  This causes electrons and holes to interact.  When this happens, the band gap energy level of an electron decreases, causing a release of energy via a photon (i.e. a particle of light).  \n\nDepending on the semiconductive material of the diode, the released photons result in different colors of light because of different band gap energy.  Here are a few examples:\n\naluminum gallium arsenide (AlGaAs) - red and infrared\n\naluminum gallium phosphide (AlGaP) - green\n\naluminum gallium indium phosphide (AlGaInP) - high-brightness \norange-red, orange, yellow, and green\n\ngallium arsenide phosphide (GaAsP) - red, orange-red, orange, and yellow\n\ngallium phosphide (GaP) - red, yellow and green\n\n-------------\n\nHope this helps
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electricity (î-lèk-trîs´e-tê), class of phenomena arising from the existence of CHARGE. According to modern theory, most ELEMENTARY PARTICLES of matter possess charge, either positive or negative. Two particles of like charge, both positive or both negative, repel each other; two particles of unlike charge are attracted. The electric FORCE between two charged particles is much greater than the gravitational force between the particles. Many of the bulk properties of matter are ultimately due to the electric forces among the particles of which the substance is composed. Materials differ in their ability to allow charge toflow through them. Those that allow charge to pass easily are conductors,  whereas those that allow extremely little charge to pass through are called insulators,  or DIELECTRICS. A third class of materials, called SEMICONDUCTORS, is intermediate. Electrostatics is the study of charges, or charged bodies, at rest. When positive or negative charge builds up in fixed positions on objects, certain phenomena can be observed that are collectively referred to as static electricity. The charge can be built by rubbing certain objects together, such as silk and glass or rubber and fur; the friction between these objects causes ELECTRONS to transfer from one to another with the result that the object losing electrons acquires a positive charge and the object gaining electrons acquires a negative charge. Electrodynamics is the study of charges in motion. A flow of electric charge constitutes an electric current. In order for a current to exist in a conductor, there must be an ELECTROMOTIVE FORCE (emf), or POTENTIAL difference, between the conductor's ends. An electric CELL, a PHOTOVOLTAIC CELL, and a GENERATOR are all sources of emf. An emf source with an external conductor connected from one of the source's two terminals to the other constitutes an ELECTRIC CIRCUIT. Direct current (DC) is a flow of current in one direction at a constant rate. Alternating current (AC) is a current flow that increases in magnitude from zero to a maximum, decreases back to zero, increases to a maximum in the opposite direction, decreases to zero, and then repeats this process periodically. The number of repetitions of the cycle occurring each second is defined as the frequency, which is expressed in HERTZ (Hz). The frequency of ordinary household current in the U.S. is 60 cycles per sec (60 Hz), and electric devices must be designed to operate at this frequency. In a solid, the current consists not of a few electrons moving rapidly but of many electrons moving slowly; although this drift of electrons is slow, the impulse that causes it moves through the circuit, when the circuit is completed, at nearly the speed oflight. The movement of electrons in a current is not steady; each electron moves in a series of stops and starts. In a direct current, the electrons are spread evenly through the conductor; in an alternating current, the electrons tend to congregate along the conductor surface. In liquids, gases, and semiconductors, current carriers may be positively or negatively charged.
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Light is an electromagnetic wave, like radio waves, governed by Maxwell's Equations:\n\nhttp://en.wikipedia.org/wiki/Maxwell%27s_equations\n\nThis means there are both electric and magnetic waves travelling together; one cannot exist without the other. The energy of the light trades back and forth between the electric and magnetic waves continuously. \n\nNeat thing to consider - metals are shiny because they are conductors! The electric field hits the metal and is cancelled out - a conductor won't allow a voltage difference between two points. The current which flows through the conductor creates a magnetic field which radiates away at 90 degrees to the source. That magnetic field collapses and creates an electric field... effectively, a new light beam! And that is how reflections work.\n\nNo conductor is perfect, of course, so some of that electric current in the surface of the conductor causes resistive heating. This is the reason why a fork left on a sunny picnic table will get a lot hotter than the surrounding air. \n\nFreakier still is that light has mass, which demonstrates that waves and fundamental forces seem to be carried by some sort of "messenger particle", though that's well outside the scope of this Electrical Engineer's theoretical physics training!
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What is photoreading?
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A solar cell (or a "photovoltaic" cell) is a semiconductor device that converts photons from the sun (solar light) into electricity. In general a solar cell that includes both solar and non-solar sources of light (such as photons from incandescent bulbs) is termed a photovoltaic cell. Fundamentally, the device needs to fulfill only two functions: photogeneration of charge carriers (electrons and holes) in a light-absorbing material, and separation of the charge carriers to a conductive contact that will transmit the electricity. This conversion is called the photovoltaic effect, and the field of research related to solar cells is known as photovoltaics.\n\nAlso check this link, this is from NASA http://science.nasa.gov/headlines/y2002/solarcells.htm
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its electrical properties
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In physics, thermal conductivity, k, is the intensive property of a material that indicates its ability to conduct heat.\n\nIt is defined as the quantity of heat, Q, transmitted in time t through a thickness L, in a direction normal to a surface of area A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.\n\nthermal conductivity = heat flow rate × distance / (area × temperature difference)\n\n\nElectrical conductance is the reciprocal of electrical resistance. It is a measure of how easily electricity flows along a certain path through an object. The SI derived unit of conductance is the siemens (symbol S, equal to 1/Ω; alias the "mho"). Oliver Heaviside coined the term in September 1885.
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Assuming you mean photoelectric and not just solar heat cells: \nThe material (silicon ore = sand) is not the problem, the trouble is the apparatus needed to electrolyse and purify the material, and then apply it to suitable carriers.
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Electro-optics is a branch of technology involving components, devices and systems which operate by modification of the optical properties of a material by an electric field. Thus it concerns the interaction between the electromagnetic (optical) and the electrical (electronic) states of materials.