LDR Working Model Physics Investigatory Project PDF Class 12: Download

LDR Working Model Physics Investigatory Project PDF Class 12

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INTRODUCTION

A photoresistor or light-dependent resistor (LDR) is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits Photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light and dark activated switching circuits. These resistors use pure semiconductors like silicon or germanium. When the light falls on the LDR, then the electrons get excited by the incident photons and move from the valence band to the conduction band and therefore the number of charge carriers increases. In other words, the conductivity goes up.

Distinction needs to be made here between photocells and LDRs. In a photocell, when it is excited by light (photons), electricity is generated. Unlike photocells, LDRs, do not generate electricity but only change their conductivity.

THEORY

A light dependent resistor works on the principle of photo conductivity. Photo conductivity is an electro-optical phenomenon in which the material’s conductivity is increased when light is absorbed by the material. Modern light dependent resistors are made of materials such as lead sulphide, lead selenide, indium antimonide and most commonly cadmium sulphide (CdS) and cadmium selenide.

When light falls i.e. when the photons fall on the material, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. 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. The result of this process is more and more current starts flowing through the device when the circuit is closed and hence it is said that the resistance of the device has been decreased. This is the most common working principle of LDR

MATERIAL REQUIRED

Cardboard
LDR
Switch
Battery- 9V
LED
Resistance: 200k Ω and 470 Ω
Transistor: 547B
Connecting Wire

PROCEDURE

Gather all necessary materials: LDR, resistor, transistor, LED, battery, battery connector, connecting wires, switch, cardboard, scissors, glue or tape, marker.
Draw the circuit diagram on the cardboard.
Position the LDR, resistor, transistor, LED, and battery connector on the cardboard according to the circuit diagram.
Secure all components in place using glue or tape to prevent them from moving.
Use connecting wires to make the necessary connections between the components as per the circuit diagram.
Connect the battery to the battery connector, ensuring the positive and negative terminals are correctly connected.
If a switch is included, turn it on to complete the circuit; otherwise, simply connecting the battery should power the circuit.
Test the model by changing the light levels around the LDR; the LED should turn on in darkness and turn off in bright light.
Observe how the brightness of the LED changes with varying light conditions.

OBSERVATION

The LED illuminated brightly when the surrounding light levels decreased significantly, demonstrating the LDR’s response to low light conditions. In complete darkness, the resistance of the LDR increases, allowing more current to flow through the circuit, thus powering the LED.
When exposed to bright light, the LED turned off completely. This occurs because the LDR’s resistance decreases in high light conditions, resulting in minimal current flow through the circuit. The transistor, which acts as a switch, does not activate, leading to the LED remaining off.
As the ambient light dimmed gradually, the LED’s brightness increased correspondingly. This illustrates a smooth transition in the response of the circuit to changing light conditions, indicating that the LDR can detect and react to subtle variations in light intensity.
The experiment showed an inverse relationship between light intensity and LED brightness. As the light intensity increased, the brightness of the LED decreased, reinforcing the sensitivity of the LDR to changes in light.
The observations confirm that the LDR can be utilized in practical applications where light level detection is crucial, such as automatic lighting systems or alarm systems.
This project provided insight into the functioning of electronic components and illustrated the practical implications of light sensors in everyday technology.

EXTENSION OF SCOPE IN FUTURE

Enhanced Security Systems: By incorporating the LDR model into advanced security frameworks, it can be used for detecting unauthorized access in restricted areas. The sensitivity of the LDR to light can trigger alarms when an intruder interrupts a light beam, ensuring enhanced security.
Energy-Efficient Smart Lighting: Automatic streetlights can be optimized using LDRs, reducing energy consumption by ensuring lights operate only during low light conditions. Future developments can include the integration of solar panels and LDRs for entirely sustainable lighting systems.
Adaptive Vehicle Lighting Systems: LDRs can be used in vehicles to create adaptive lighting systems where headlights automatically adjust their intensity based on surrounding light levels, improving road safety and driver comfort.
Interactive Devices and Gadgets
LDRs can be incorporated into interactive devices such as light-sensitive toys, educational kits, or artistic installations where changes in light can produce dynamic visual or audio effects.
Disaster Warning Systems: LDRs can be integrated into early warning systems for natural disasters like wildfires, where changes in light intensity caused by smoke or flames could trigger alarms.
Solar Energy Management: LDRs can assist in optimizing solar panel positioning to maximize energy capture by detecting the direction of maximum light intensity.

CONCLUSION

The LDR Working Model successfully demonstrates the fundamental principles of light-dependent resistance and its practical applications. Through the project, the response of the LDR to varying light intensities was observed, highlighting its potential in automating systems based on light levels.

The project illustrates that the resistance of an LDR decreases with increased light intensity, allowing it to control the current flow in a circuit. This principle was effectively applied to create an automatic streetlight switching circuit, where the LED turns on in low light and off in bright light conditions.

This experiment emphasizes the practical utility of LDRs in diverse applications such as energy-efficient lighting, security systems, and interactive devices. Moreover, it provides insights into the simplicity and versatility of electronic components, fostering a better understanding of sensor-based systems and their importance in modern technology.