 Welcome to the session. Today's topic of the discussion is the light dependent registers, that is LDR and the solar cell. My name is Ajit Subha Srinishi, working as an assistant professor in the electronics telecommunication department at Walchin Institute of Technology. So what will be the outcome of this today's session? At the end of the session, students will be able to select the appropriate transducers to measure the physical parameters like light intensity and converts the light intensity to the power. So before we proceed further into the session, what should the basic knowledge you should possess, that is, you should have the knowledge of the different material, that is its property, especially the electrical property. So electrical properties are the materials are classified based on the electrical property as are the insulators, semiconductors, metals. So you should have knowledge of that and what should be the conductivity of the metals, semiconductors, and the insulators. So knowledge of the electrical circuit analysis, which is at the basic level. So LDR, light dependent resistors. So what does mean by the LDR? Light dependent resistors name itself suggests it is a resistor, which will converts the light falling on into the equivalent resistance. So resistance changes, which is resistance is directly proportional to the light intensity. So more will be the light falling on this LDR, less will be the resistance. So this LDR is basically, which is also called as a photo resistors or a photo cells. Photo resistors in the sense that resistors changes with the light intensity falling on it and cell in the sense that when you connect these resistors with another external energy source, it will act as a variable voltage. So cell in that sense and the resistance in this sense. So this will be the symbol of the LDR, that is light dependent resistors. This is a symbol of the light falling on it and this is one of the actual image of the LDR. So this is your LDR material that is semiconductor materials and these are the two lids. So it is a two junction devices that is two terminal devices. So construction, so construction of the LEDs is mostly from the semiconductors. So no metal is used here, no insulator resist, only the semiconductor materials are used, commonly used are the light sulfide and cadmium sulfide nowadays is mostly recently used for the construction or formation of the LDR. So this, as you can see, these are the two different leads or junctions, so which is connected with the metal and this is actual semiconductor material that is cadmium sulfide on this. And on this top of this, there is a anti reflection glass coating. So whatever is the light falling on it, it will get absorbed on this material and there will be no reflection from it. So at this two end you will get the variable resistance due to the variable intensity light falling on it. Now types of the LDR, LDR are classified in two types that is intrinsic and extrinsic type. So in the intrinsic type of your semiconductor material is used that is silicon, germanium or simply the cadmium or any other gallium also. So simply the semiconductor material without any mixture or without any alloy or mixture is used, compound is used. And in the extrinsic type of the semiconductors, metals are mixed to that is impurities added in that. So difference between these two intrinsic and extrinsic is that the conductivity of the extrinsic material is enhanced as compared to the intrinsic material. And also the bandgap of the extrinsic type LDR is less as compared to the intrinsic type of the, intrinsic type of the LDR. So extrinsic type of the LDR allows us to have a different concentration of the impurities and also allows the different band gaps. So this will make us more versatile and extrinsic type of the LDR is most commonly used. Now working of the LDR is when light falls on the LDR light dependent resistors. So most of the electrons that is switches in the valence band will be the jump into the conduction band. And as the most of the electrons in the conduction band, the conductivity of that particular, conductivity of that LDR devices increases, conductivity increases means resistance decreases because resistance is inversely proportional to the conductivity. So as the conductivity increases, resistance decreases. Similarly, when no light fall on it, there will be the high resistivity because semiconductor material, when there is no energy excitation from the valence band to the conduction band, it will act as an insulator that it will present a high amount of the resistance. Now this is the characteristics of the LDR. If you see, this is a dark when there is no light falling on it. So this characteristic is the resistance versus the intensity which is measured in the lux. And this left side and head side is the, what it is called as a less intensity that is a dark side. And this is a thousand. That means during the daylight, you observe the thousand, typically thousand lux of the intensity during the daylight. And if you see the dark value of the resistances, which is very high, which is an range of the 10 raise to eight, it is greater than the mega ohm. And when full light during the sunlight, you can see the resistance value which is coming into the two digit number which is an order of the 10 ohm. And also you can observe that this relation that is inversely proportional, this resistance is inversely proportional to the light intensity. Coming into the, what do you think what should be the value of the LDR when ideal value of the LDR when light falling on it or also when no light is falling on it? So what should be the ideal dark value of the resistance of the LDR? And what should be the value of the LDR when light falls, full light falls on it? Think about it, pause this video, write the value, these those values on the paper. So this value should be the dark value should be the infinity. So this should be the infinity. And when full light falling on it, daylight falling on it, it should the value should be the zero. This, these are the two ideal values of the LDRs applications. Now application of the LDR is one of the automatic emergency light when there is a dark. The, that will dark will be sensed by the LDR and it will turn on the emergency light which is running on the batteries. Audio compressor also a fire alarm and automatic street light in the automatic street light light will be turned on and off during the, it will be the turn on during the night and it will be the turn off during the day by sensing the light with the help of the LDR. Now solar cells. Solar cells are the solar cell which is also called as a photovoltaic cell and which is a electrical device which will converts the light falling on it into the equivalent electricity or equivalent current. So as the voltage remains constant because this is a voltage, only the current is a, current is a directly proportional to intensity when light intensity falling on it, solar cell is increases, current also increases. So which is called as a physical and chemical phenomena which is observed in the solar cell. So solar cell is also called as photovoltaic cell and this will be the symbols. This is a battery symbol. If you see carefully, battery symbol positive or negative and light fall on it. So construction of the cell or cell again semiconductor materials are used and two different types of the materials are used that is P type and N types in the P types, majority carriers are the holes and in the N types, majority carriers are the electrons. So when light falling on this structures, electron will pair is generated. So this is a P type material, P type layer and this is a N type layer and commonly used material is the silicon and also the gallium arsenide is also now used in the solar cell nowadays. Working. So in the working, when light falling on it, it will get absorbed and this light absorbed is used to have, it will gain the energy that is electron in the valence band will gain the sufficient energy to cross or coming to the conduction band and in this way, the electron hole pairs are generated. So absorption of the light and generation of the electron hole pair add the boundaries of the PN junction. So hole with the generated in the P type material and electron will be the generated in the N type material and this electron hole pair. So last stage will be the separation. This electron hole pairs are get separated from the junction. So this by this three phenomena, you can explain the working of the solar cell that is absorption generation of the electron hole pair at the junction that is PN junction and the separation of that electron hole pair that will constitute the current. Now solar cell formation, solar panel formation in the solar panel formation, there is a single cell and the single cells are connected into the series and parallel combination and forming one panel. Again, this panel is connected again into the series and parallel depending upon whatever is the voltage and current requirement. If the voltage requirement is more, cells are connected in the series if the voltage current requirement is more, the cells are connected in the parallel. Now this is one of the typical application as a photovoltaic system as you're generating the electricity. So this will cell have a generator and it has amplitude that is maximum power tracking system and inverter because the power generated is a DC it need a inverter for it. So generating power, this is one of the example of the photovoltaic system. Now application, there are different applications. Satellite in the satellite solar panel it is used and most of the applications are the power generation. It is on grid power generation, off grid power generation, rooftop power generation. So these are the applications of the solar cells. These are the references. Thank you.