physics investigatory project- LDR. IATION ‘N LDR CONCLUSION Based on the obsewation above, it eam be cometuded that the LDR based. INTRODUCTION • A light dependant resistor(LDR) or a photoresistor or photocell . Physics Investigatory Project on LDR as Variable Resistor. Project Report Submitted On Light Dependence Resistance  Submitted By: A. Varun Class â XII Kendriya Vidyalaya no. 2 Pondicherry.

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One of the most common uses for transistors in an electronic circuit is as simple switches.

Vehicle counter at traffic check posts. For the automatic switching, we have used the following circuit consisting of Transistors. But when light falls on the LDR, the LDR starts conducting and the net base voltage of transistor T1 crosses the threshold voltage, causing T1 to fire. Therefore the circuit is complete through the kilo-ohms resistor and the led will glow. Conclusion Based on the observation above, it can be concluded that the LDR based electronic switch can be successfully deployed for the following applications: Projedt at this time, 4V DC reach at base of transistor T 2invetsigatory that emitter has highly negative voltage in comparison of its base, so that transistor T 2 highly conducts.

Discussion Investigatody the relationship between the resistance of the LDR and lrr light intensity? Click here to sign up. But resistance of 1. Cu photoconductors are among the best far- infrared detectors available, and are used for infrared astronomy and infrared spectroscopy. Select the bulb with the lowest power rating and connect it to the holder as shown in the figure. In the society, some times street lights glow in day time due to any reason.

The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. Repeat these steps with different power sources at different distances and note down observations. Applications The internal components of a photoelectric control for a typical American streetlight. It consists of emitter, base, and collector.


In de- energized condition, position-1 will be active and in energized condition, position-2 will be active. A photoelectric device can be either intrinsic o extrinsic. Photoresistors come in many types. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits Photoconductivity. Remember me on this computer. If incident light on a photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band.

Light Dependent Resistance, Physics Project Report Light Dependent Resistance, Project Report LDR

Remember me on this computer. The transistor circuit described later is connected to a relay which is in turn connected to an external buzzer.

Theory Alight dependent resistor works on the principle of photo conductivity. This is the most common working principle of LDR. The collector of transistor T 2 has positive voltage by relay coil. Needless to say, one has also to install a stealth switch that is known only to the owner so that the owner can disable it for his own entry. Photo resistors have been seen in early forms since the nineteenth century when photoconductivity in selenium was discovered by Smith in The LDR resistance decreases with increase in intensity of light and hence there is an increase in the flow of current.

People Counter at Auditoriums 4. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon.

Venkatakrishnanfor his vital support, guidance and encouragement, without which this project would not have come forth. Ambient light falling on the photoresistor causes the streetlight to turn off. Alka Chopra as well as our principal R K Tyagi who gave me the golden opportunity to do this wonderful project on the topic Write the topic namewhich also helped prkject in doing a lot of Research and i came to know about so many new things I am really thankful to them.


This puts the relay switch in position-2, which cuts off the buzzer. However, prolonged exposure should be avoided which can damage the skin and eyes.

Light dependent resistor(LDR) – physics investigatory project

I would like to thank my parents who helped me in gathering diverse information, collecting data and guiding me from time to time in making this project, despite their busy schedule. When light is cut off, the base voltage of T1 falls back to less than the threshold voltage of its base —emitter junction and therefore, the relay gets de-energized. By using laser, it can be used for safety purposes.

When the circuit is powered, the relay goes to position-1 to which the buzzer is connected. Due to use of it, we can solve above problems and can also save investigahory and men’s power.

These resistors use pure semiconductors like silicon or germanium. We use a transformer of V for the circuit. The error lies within the experimental limit.

The intensity decreases as the distance from the source increases 4. When DC voltage comes through the base of transistor, the current starts to flow through the emitter of transistor and completes the circuit to the negative end of the DC voltage. Connect the LDR, battery 6V and the multimeter in series.