INDEX Aim Components Brief Description of components

Circuit Diagram Working Advantages Uses Precautions Bibliography

AimTo investigate the use of LDR(Light Dependent Resistor)in Twilight Switch.

ComponentsA Light Dependent Resistor(LDR)

Battery

Battery Clip

Carbon Resistors

Transistor 1015

Transistor 3904

Buzzer

LED

Preset

Brief Description 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.

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.

3. LDR:- LDR means light dependent resistance which is used to complete the circuit. Light Dependent Resistance [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.It is made up of Cadmium Sulphide.The resistance of LDR is 10 MΩ(in full dark) and to about 10-4MΩ(in day light).

4. Battery:- It provides DC electric supply of 9 volts in the circuit.

5. Preset :- A preset is a three legged electronic component which can be made to offer varying resistance in a circuit. Such variable resistors are

commonly used for adjusting sensitivity along with a sensor.

6.LED:- An LED(Light Emitting Diode) is connected to the circuit when LDR comes in the darkness.

Circuit Diagram

9V

D.C

TR1

1015

TR2

3904

BUZZERLED

LDR

PRESET

WorkingThe L.D.R has been used in the input base of p-n-p transistor 1015(TR1). L.D.R whose value depends on the intensity of light incident on it,is connected to preset of 100KΩ which is further connected to 22KΩ resistance.The other point of L.D.R goes to positive terminal of the battery.Collector of the second transistor n-p-n 3904(TR2) is connected to L.E.D and other point of bulb goes to positive terminal.A resistance is also connected between base and emitter of TR2.Whenever light falls on the L.D.R ,its value decreases and at that moment we get output voltage on collector of the n-p-n transistor.A D.C bulb is connected between collector(n-p-n) and positive supply .This positive voltage is controlled by the preset 100KΩ.

The preset is adjusted in such a way that on obstructing light over L.D.R, the L.E.D is put ON while it remains OFF when kept in light.This project requires 9V D.C supply by a battery.

AdvantagesCollection of parts of the circuit are

easily available.Accuracy of this circuit is more than

accuracy of other circuits.By using laser, it can be used for

security purposes.It can be used to stop the wastage of

electricity.The cost of circuit is low.This circuit saves the men's power.

UsesIt can be used in street lights.It can be used in mines areas.By using laser, it can be used for

safety purposes.It can be used in houses.It can be used in jail lights.

PrecautionsThe source of light must be

adjusted so that light falls normally on L.D.R.

Source of light must radiate light continuously.

Connect L.D.R carefully to the voltage source.

BIBLIOGRAPHYPhysics Lab Manual –Rachna

PandeyPhysics Textbook-NCERTPhysics teacher-Mr.Jitendra

SinghGoogle India(Website)-

www.google.co.in