Una Resistencia Sensible a la Luz. Fotoresistencia (LDR)

Understanding Photoresistors and Their Applications

What is a Photoresistor?

• A photoresistor, also known as an LDR (Light Dependent Resistor), is an electronic component whose resistance varies with light exposure. The more light it receives, the lower its resistance becomes.

How Does a Photoresistor Work?

• The operation of a photoresistor is based on the photoelectric effect, utilizing semiconductors like cadmium sulfide (CdS). When photons hit the material, electrons gain energy and move to a conduction band, enhancing conductivity.

• Resistance changes in response to light have a delay, making photoresistors unsuitable for high-speed applications such as communications. Alternatives like photodiodes or phototransistors are recommended for those uses. However, they are effective in slower systems like automatic public lighting.

Building a Circuit with a Photoresistor

Components Used

• The experiment involves connecting two 1.5V batteries in series to create 3 volts and using crocodile clips for circuit assembly. A 120-ohm resistor is included to limit current flow and protect both the photoresistor and LED from damage.

Circuit Assembly Steps

• The circuit includes connecting the photoresistor and an LED (light-emitting diode) where the longer leg connects to positive voltage and shorter leg connects to negative voltage. Ambient light conditions are adjusted for better visibility of results during testing.

Observing Light Sensitivity

Testing Light Response

• As ambient light decreases, illuminating the photoresistor with a lamp shows that increased light leads to higher current flow through the circuit, causing the LED to shine brighter. This demonstrates how resistance drops with increased illumination levels.

• Blocking the flashlight reveals that when less light hits the sensor, current decreases accordingly; this relationship illustrates how resistance affects current flow through varying light conditions. Additionally, sensitivity extends beyond visible light into ultraviolet ranges as well.

Advanced Measurements Using Current Meters

Measuring Current Flow

• Replacing the LED with a milliammeter allows measurement of current intensity flowing through the circuit under different lighting conditions; blocking ambient light reduces readings significantly while bringing closer increases them due to reduced resistance in LDR circuits.

Utilizing Infrared Detection

• An infrared LED is introduced into testing by placing it at one end of a black tube designed to filter out unwanted environmental light; this setup confirms that photoresistors can detect infrared radiation effectively as indicated by needle movement on measuring instruments when exposed to IR signals from remote controls.

Final Observations and Measurements

Connecting Digital Multimeter

• The final step involves connecting the photoresistor to a digital multimeter set on a scale capable of measuring up to 20K ohms; this allows for precise measurements of electrical magnitudes such as voltage or resistance under various lighting scenarios encountered throughout experiments conducted earlier in this session.