Photo Conductive Cell

Introduction to photo conductive cells:

Photo conductive means that it operates on light energy. The photo resistor is also made to work as the photo conductive cells. The resistivity of the photo resistor changes as the illumination of the incident light changes. This effect is called the photoconductivity effect. They are also called the light dependent resistors (LDR). Let us discuss the photo conductive cells.

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Need for Photo conductive cells


The photo conductive cells are the devices, which are used for detecting and measuring the electromagnetic radiations. It is based on the principle that the conductivity of the photo conductive cell changes as the wavelength or the frequency of the incident light changes. The photo conductive cell has two terminals, which are connected to a very thin coating of the photo conductive material.

Examples of Photo conductive cells


The main examples of the photo conductive material are Cadmium Sulphide (CdS), Cadmium Selenide (CdSe), Lead Selenide, Lead Telluride and Indianoid. The coatings of the photo conductive materials contains some impurities like antimony, Indium nitrate etc, for improve the efficiency of the photo conductive cell. The conductivity of the photo conductive cell is directly proportional to the concentration of the charge carriers present in the photo conductive material. As the light energy falls on the photo conductive cell, the covalent bonds of the semiconductor breaks and then create the electron hole pair. Due to this, the current carriers decrease the resistance of the material. In the absence of light, the resistance of the photo conductive cell is maximum. This current is called the dark current and the resistance corresponding to this current is called dark resistance. The dark resistance may be as high as few under mega ohms. Is this topic Equation of Work hard for you? Watch out for my coming posts.

Conclusion for the photo conductive cells


The light sources are placed one by one (decreasing order of wattage) at the fixed distance from the LDR. The ammeter readings are taken in each case. This is repeated and another set of reading obtained by varying resistance in the box. Keeping the distance and the bulb used the same; various color filters are held before the source. When exposed to, light the resistance of the photo resistor decreases and a large current called joint current flows through it.