Lab Report 5

pdf

School

University of Illinois, Urbana Champaign *

*We aren’t endorsed by this school

Course

212

Subject

Electrical Engineering

Date

Feb 20, 2024

Type

pdf

Pages

Uploaded by AmbassadorFireToad18

Kitchen Sink Names & NetID: Ravyn Edran (redran2), Josh Frye (jcfrye2), Aidan Stahl (ahstahl2), Tuna Tuncer (ttuncer2), & Zhengze Cao (zhengze2) 28 September 2023 Lab Report 5 Introduction The purpose of this lab is to determine if an LED is considered Ohmic. We test the claim that LED bulbs are ohmic across the entire voltage output range of the DAC & can be treated as ideal resistors. This is done by connecting an LED and resistor in series (figure 1) and measuring the voltage at different points across the system. Then we can conclude that LEDs also follow Ohm’s law. This can be found by determining if the LED has a consistent and non-changing resistance. Our team expects the LED to be ohmic since it consumes power like a resistor. Group Dynamic In this lab the first action we took to improve our ability to work as a group was switching around who did what. This time the people who normally wrote most of the lab reports collected data and visa versa. This was done to ensure that everyone was gaining experience in all areas of the lab. The second action we took we allow other group members to create the procedure for the lab. Normally the same people create the procedure for the lab and carry it out, however this time we decided to switch who did what to ensure that everyone has an understanding of what was actually being done in the lab. Methods To complete this lab we set up the resistor and the LED in series with each other. We collected the voltage above the resistor and between the resistor and LED (figure 2). We will determine

the current passing through the resistor using Ohm’s law. Due to the fact that the resistor and LED are in series, they will have the same current. Using this data and the voltage of the DAC we will be able to determine if the LED has a constant resistance and is therefore Ohmic. If the voltage and therefore current stay the same then the LED will be Ohmic. 𝑉 = 𝐼𝑅 𝑉 1 = 𝑉 ?𝐴? 𝑉 1 = 𝑉 𝑅2 + 𝑉 𝑅1 = 𝐼𝑅 2 + 𝐼𝑅 1 In series: 𝐼 1 = 𝐼 2 Results

Discussion The data we collected is the voltages above and below the resistor. This will allow us to determine the potential difference across the resistor. The voltage below the resistor will always be 0 because it is ground. By finding the voltage above the LED we can find the voltage drop across the LED because it will be V 2 -0=V 2 . This is important because it can find if the voltage drops and therefore current stays consistent across the LED. We found that the current changed as we increased the voltage on our DAC. Conclusion We disproved the claim that LEDs are Ohmic devices and this also disproved our expectations. Based on our findings LEDs are not ohmic because they don’t follow Ohm’s law and the curve plotted isn’t linear. To find this, we connected a 1000-Ohm resistor in a series with an LED. Then we started with a low DAC output and increased the DAC output until we got to three volts. We found the voltage at the points above the resistor and LED (V1) and below the resistor but above the LED (V2). We subtracted these voltage values to find the potential difference across the resistor alone. Because I = V/R, we calculated the current across the resistor and LED (since they are in series) for each voltage output. Until around 1.7 volts, the potential difference across the resistor was 0, meaning no current was flowing. At around 1.7 volts, the LED turned on. After the LED turned on, we found the potential difference across the resistor to increase with each DAC output increase because V1 increased, while V2 remained constant. Because the voltage across the resistor is increasing and I = V/R this means that the current across the series resistor and LED continues to increase as the DAC output increases. However, we found that V2, the potential across the LED, remained constant. Since Ohm’s law shows a linear relationship between voltage and current, but the voltage remained constant even as the current increased, this demonstrates that LEDs do not follow Ohm’s law and are, as a result, not Ohmic.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version