Light dependent resistor(LDR) - physics investigatory project

Project Report Submitted On Light Dependence Resistance

Submitted By: A. Varun Class – XII

Kendriya Vidyalaya no. 2 Pondicherry University Campus Periyakalapaet, Pondicherry – 605014

A PHYSICS PROJECT “LIGHT SENSOR AND DARK SENSOR USING LIGHT DEPENDENT RESISTOR”

By Varun A Of Class XII

Certificate This is to certify that Varun A, student of Class XII, Kendriya Vidyalaya Pondicherry university campus has completed the project titled LIGHT DEPENDENCE RESISTANCE during the academic year 2012-2013 towards partial fulfilment of credit for the Physics practical evaluation of CBSE 2013, and submitted satisfactory report, as compiled in the following pages, under my supervision Mr. Venkatakrishnan, Department of Physics, Kendriya Vidyalaya Pondicherry university campus, Pondicherry.

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Acknowledgements "There are times when silence speaks so much more loudly than words of praise to only as good as belittle a person, whose words do not express, but only put a veneer over true feelings, which are of gratitude at this point of time." I would like to express my sincere gratitude to my physics master Miss. Venkatakrishnan , for his vital support, guidance and encouragement, without which this project would not have come forth. I would also like to express my gratitude to the staff of the Department of Physics at Kendriya Vidyalaya Pondicherry university campus for their support during the making of this project.

(((A.Varun)))

INTRODUCTION In the society, sometimes street lights glow in day time due to any reason. In mines area people face many difficulties due to absence of light in the nights. In frontier and hilly areas, people face many problems due to damaged street lights. 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. Due to use of it, we can solve above problems and can also save electricity and men's power.

PRINCIPLE This project is based on Light Dependent Resistance (L.D.R.).LDR is a resistance, in which opposing power of current depends on the presence of quantity of light present, i.e. the resistance of LDR increases or decreases, according to quantity of light which falls on it. If LDR places in darkness, the resistance of LDR increases and when light falls on it, the resistance of LDR decreases and act as a conductor. Any LDR in the presence of light and darkness changes its resistance is depending on the different types of LDR.

BRIEF DISCRIPTION OF COMPONENTS 1. TRANSISTOR: When a thin slice of p-type is sandwiched between two blocks of n-type, then n-p-n transistor is formed. It consists of emitter, base, and collector. In the project, common emitter n-p-n transistor (BC-547) is used.

2. CARBON RESISTOR: A carbon resistor has generally four rings or bands A, B, C and D of different colours corresponding to the value of resistance. In project, we use carbon resistance of two 100 kilo-ohms, 470 ohms and 330 ohms.

3. LDR: LDR means light dependent resistance which is used to complete the circuit.

4. LED: A light-emitting diode (LED) is a semiconductor light source. When a light-emitting diode is forward-biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. In this project, we use led of white colour.

5. BATTERY: This is a rectangular prism shape with rounded edges and a polarized snap connector at the top. In project, we use 9-Volt battery. 6. WIRES: A wire is a single, usually cylindrical, flexible strand or rod of metal. These are used to connect components.

Aim (a) Dark sensor using L.D.R, led, battery, transistor and a few resistors.

(b) Light sensor using L.D.R, led, battery, transistor and a few resistors.

Circuit Diagram (a) Dark Sensor

(b) Light Sensor

WORKING (a) Dark Sensor Let 9V-DC is flowed in the circuit. When light falls on LDR then the resistance of LDR will decrease and approximate equal to 10 ohms. 9V DC comes from 330 ohms resistance and passes through an LED to the collector end of the BC-547 transistor. Also 9V DC comes though a 100 kilo-ohms resistance to one end of LDR and to the base of the transistor. 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. Another end of the 100 kiloohms resistor is connected to the emitter. When light falls on the LDR, the resistance offered by the LDR is very high (nearly millions). The current will not flow through the LDR and the circuit won’t be shunted. Therefore the circuit is complete through the 100 kilo-ohms resistor and the led will glow. When no light falls on the LDR, the LDR offers very low resistance (nearly 10 ohms) and the circuit is shunted and therefore the led doesn’t glow. The LDR is also connected to minimise the current flow to the battery.

USES • It can be used in street lights. • It can be used in mines areas. • It can be used in hilly areas. • It can be used in frontier areas. • It can be used in houses. • It can be used in jail lights. • By using laser, it can be used for safety purposes.

(b) Light Sensor Let 9V-DC is flowed in the circuit. When light falls on LDR then the resistance of LDR will decrease and approximate equal to 10 ohms. 9V DC comes from 470 ohms resistance and passes through an LED to the collector end of the BC-547 transistor. Also 9V DC comes though one end of LDR and the other end to 100 kilo-ohms and to the base of the transistor. 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. Another end of the LDR is connected to the emitter. When light falls on the LDR, the resistance offered by the LDR is very high (nearly millions). Therefore the circuit is not complete and the led will not glow. When no light falls on the LDR, the LDR offers very low resistance (nearly 10 ohms) and therefore the led glows. The 100 kilo-ohms is connected to minimise the current flow to the battery.

USES • By using laser, it can be used for safety purposes. • It can be used to find the intensity of sunlight falling on the LDR. • It can be used in mines areas for current indicator using another light. • It can be used in hilly areas. • It can be used in houses. • By using buzzer, it can be used for security purposes in jails.