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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For conduction, emitter has some negative voltage in the comparison of its base. A photoresistor can be applied in light-sensitive detector circuits, and light and dark activated switching circuits. At night, the heater cools, closing the power contacts, energizing the street light. When DC voltage comes through the base of transistor, current starts to flow through the emitter of transistor and completes the circuit to the negative end of the DC voltage.

But the moment, the light source is interrupted, lnvestigatory buzzer will start ringing.

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

A common usage of this application can be found in many guitar amplifiers that incorporate an onboard tremolo effect, as the oscillating light patterns control the level of signal running through the amp circuit. By using laser, it can be used for security purposes. Connections may be faulty. Enter the email address you signed up with and we’ll email you a reset link.

It can be used in mines areas. Now, the above terminal of 1. This intruder alarm can be easily set up in houses, banks, schools etc. This de-energizes the relay and puts it to position-1 and the buzzer starts ringing. In a photocell, when it is excited by light photonselectricity is generated.


Much useful work was conducted by T. R, led, battery, transistor and a few resistors. In mines area people face many difficulties due to absence of light in the nights.

Repeat these steps with different power sources at different distances and note down observations. In frontier and hilly areas, nivestigatory face many problems due to damaged street lights. Hence when light having enough energy strikes on the device, more and more electrons are excited to the conduction band which results in large number of charge carriers.

Another end of the kilo-ohms resistor is connected to the emitter.

For solve above these problems, we create a device in which the lights glow in night and in day time, they off automatically and don’t glow. 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. When no sufficient base voltage is present, the switch is off. Page 21 of 23 Biblography 1. It conducts when forward biased and does not conduct when reverse biased.

Table of observations S. In short, a transistor conducts current across the collector- emitter path only when sufficient voltage is applied to its base. This circuit saves the men’s power. Due to absence of positive voltage at base, emitter hasn’t negative voltage in the comparison of its base, so that transistor T 1 don’t conduct and no current flows through it.


The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. As such we can connect many devices to the relay such as sirens, flashing lights or even an automatic dialer to the nearest police station.

This is an example of an extrinsic semiconductor.

Light dependent resistor(LDR) – physics investigatory project

One of the most common uses for transistors in an electronic circuit is as simple switches. Accordingly the device is purely passive. These are used to connect components.

But at this time, 4V DC reach at base of transistor T 2so that emitter has highly negative voltage in comparison of its base, so that transistor T 2 highly conducts.

Needless to say, one has also to install a stealth switch that is known only to the owner so that inveestigatory owner can disable it for his own entry. DC reaches at pfoject of transistor T 2. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon.

Select the bulb with the lowest power rating and connect it to the holder as shown in the figure. It can be used to find the intensity of sunlight falling on the Investigatorj.