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Figure 6.2 Set up for diode meter check Figure 6.3 Set up for Blue LED meter check Figure 6.4 Set up for Red LED meter check Group No. 1 Section: 2ECE - D Group Members: Date Performed: November 25 , 2019 ABELLERA, Beaver AGPOON, Rey ARCIGA, Erica AUDITOR, Maricar Experiment No. 6 OPTOELECTRONICS OBJECTIVES:
- To obtain the response of the LDR with illumination intensity and wavelength
- To obtain the two diode conditions using an LED and a silicon diode SET-UP PHOTO Figure 6.1 Experimental set-up
DATA AND RESULTS
Part I. Response of the LDR Resistance when exposed to light: 1.66K ohms Resistance when covered: 31.22K ohms Part II. Response of the LDR with Varying light Intensity (record at least 5 data points) Table 6. 1 LDR in Varying Light intensity Red LED Blue LED V (Rs) (measured) Vout (measured) V (Rs) (measured) Vout (measured)
- 83mV 1.984V - 87mV 3.308V
- 152mV 2.028V - 221mV 3.457V
- 217mV 2.144V - 340mV 3.839V
- 889mV 3.914V - 889mV 4.006V
- 2, 482mV 4.121V - 2, 272mV 4.185V Figure 6. 5 Scatter plot of Vout with respect to I for Red LED y = 924.71x + 2. R² = 0. 0
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2
3
4
5 0 0. 0 0 0 5 0. 0 0 1 0. 0 0 1 5 0. 0 0 2 0. 0 0 2 5 0. 0 0 3
RED LED
Conclusions Based on the research conducted by the group, we therefore conclude that when using the LDR (light dependent resistor) or the photoresistor, the component would have a lower value for its resistance when exposed to light compared to having a more dim environment. This is due to the LDR’s components being semi-conductors which has a high resistance thus making electrons have a hard time moving around. Also the group therefore concludes that when using blue and red LEDs, the photoresistor would have more resistance with the red LED compare to the BLUE led. This is determined by the energy an electron loses as it moves from one side of the LED to the next. From the third part of the experiment, resistance and diode were check and compared in terms of forward and reverse bias. The fact that the direction of external voltage applied in reverse bias is the reciprocal of external voltage applied in forward bias is supported by the results of the experiment. When voltage is applied in a forward biased diode, current passes and the LED lights up while when it is reversed bias, the LED do not light up because current is not allowed to pass. POST LAB QUESTIONS
- Name applications of the LDR with discussions.
- One application of LDR is on a Security System on cash boxes or vault found in malls or banks. Since cash boxes and vaults are initially closed, it will be dark and the initial reading of resistance of the LDR will be low. This means that when an intruder breaks open the vaults, the LDR will suddenly increase resistance, and this will cause the alarm in the vaults to activate. It is also used in automatic street lights. To conserve the energy consumed by street lights, it must be turned on only when it is dark, or when cars are passing through. Street lights used LDRs to sense if it is dark in the streets, and automatically turn on. And when it is already bright, the LDR will give a high resistance which can be used to turn off the street lights.
- Name other optoelectronic devices and discuss how they work. Show diagrams for illustration.
- Other optoelectronic devices are photo diodes, optical fibers. Photo diodes are semiconductors that generate potential difference when light hits the junction. It is composed of an active N-P junction with a reverse bias operation. As the photon strikes the photo diode with an energy huge enough, an electron hole is created and diffuse in the junction to form an electric field.
- Optical fibers, on the other hand, are composed of a plastic and a transparent fiber made of glass slightly thicker than a human hair. These fibers functions as light pipe that transmit light at the two ends of the fiber. It is composed of a core, a cladding, and a buffer. The core is where the light is transmitted, the cladding prevents the light from total internal reflection, and the jacket is the protective layer of the fiber from physical damages. These fibers are used because they have higher bandwidths, less signal disruptions, weightless, and is flexible compared to copper wires.
- How do solar cells work?
- Solar cells are composed of p-type silicon place on top of the n-type silicon. N-type silicon has an excess electron while p-type silicon has an excess positively charged holes. At the junction of these silicon, called the depletion zone, the electrons can move. When sunlight strikes the solar cell, the electrons in the silicon gets ejected, and escaping electrons creates holes. This makes the electric field move the electrons from the n-type to the p-type silicon. When these silicon are connected to a metal wire, the electrons will have a path. It will travel from the n-type, crossing the depletion zone, traveling to the p- type, to the external wire, and back to the n-type to create a flow of electricity. Diagram showing how light is transmitted in an optic fiber Movement of electrons in a photo diode as light strikes the diode
