Lab 6 Report

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Northeastern University *

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242

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Electrical Engineering

Date

Feb 20, 2024

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pdf

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Uploaded by Calliefeltner1

Lab 6: Function Generator and the RC Circuit PI: Grant Wheeler DA: Will Knight Researcher: Callie Feltner Introduction: Will Knight (DA) In this lab we investigated the time it takes for a capacitor to charge and discharge, through several experiments and trials we were able to see what factors resistance, capacitance, amplitude, and frequency played on the charge time. Procedure: Callie Feltner (Researcher) To start the experiment, we assembled a function generator that would be used to collect data. A light bulb was connected to the output, and the “offset” and “amplitude” settings were adjusted until our bulb began receiving power. We measured the voltage across the bulb using the Oscope. Researcher 1: Based on the sketch of the voltages above, we deduced that turning the “offset” knob resulted in the bulb shining brighter when turned towards the maximum setting and minimum setting. We found that the light bulb was dimmer when the knob was turned near the center. The “ offset ” controls the voltage corresponding to ground. The amplitude knob worked similarly. It was determined that the amplitude value is highest when the voltage is also highest. At the lowest amplitude, the voltage was at its lowest value as well. In the center setting of the amplitude knob, it returned to the initial steady state and there did not appear to be a difference in voltage. The charging and discharging times were calculated by adding V low to ΔV multiplied by a constant.

After the initial set up, we adjusted the frequency, making some amplitude adjustments which caused the bulb to flash. To observe the function generator, settings were adjusted to predict changes in the behavior of the bulb. Then, we removed the lightbulb and added a series circuit that had a resistance and capacitance box. We measured the capacitor's voltage and adjusted the resistance values and frequency to get the shape of the plot we desired. Our RC circuit is represented below. Researcher 2: This connection was determined to be the most accurate measure of the voltage of the capacitor by the group. The Oscope probe was attached to the middle connection place of the capacitance box to measure the voltage of the capacitance by recording directly before the current makes it to the positive end of the capacitor. The charging time was measured using the cursor tool on the Oscope. We started by adjusting the resistance, leaving all other variables constant. We recorded the charging time, discharging time, voltage (high and low), and frequency. This trial was completed five times total. Our next set of trials consisted of adjusting the capacitance value and keeping the resistance consistent. This trial was repeated four additional times. The main goal of this lab experiment was to determine the answer to four questions given in the lab guide. Firstly, aimed to determine whether the charging time was smaller or larger than the discharging time. Secondly, we worked to determine how charging time behaves in relation to the voltage of the power supply. Thirdly, we observed how resistance affected charging time. Lastly, we looked at how capacitance affected charging time. Any random uncertainty in this lab was negated as an aid in understanding how to work the new equipment. Analysis: Will Knight (DA)

DA 1: Generate graphs for the data assigned to questions C and D. Are linear fits appropriate? If so make sure you include the equation of the best fit. Linear fits are appropriate in this case due to the linear behavior of the data. DA 2: Questions A and B are much more difficult to answer conclusively because it quickly APPEARS that 𝜏 = 𝜏?𝑖?? ℎ 𝑎?𝑔? and that 𝑉 ℎ 𝑖𝑔 ℎ and 𝑉𝑙𝑜𝑤 make no difference to 𝜏 . What steps did your group complete to double check that you did not overlook some small difference in investigating questions, A and B. To observe the effect that the amplitude had on 𝜏 , we set the resistance and capacitance to a constant value and manipulated the Voltage. This allowed us to change the distance between the V low and V high . Although 𝜏 varied as we increased the amplitude, there was no discernible pattern and not enough difference in the data to make a difference. Conclusion: Grant Wheeler (PI) The goal of this lab was to examine the relationship between the charge and discharge values of 𝜏 on a capacitor. After conducting this lab, it was found that the charging time of 𝜏 on a capacitor was greater than the value of the discharge time when the resistor value was low, but the discharge was larger than the charging time when the resistance was higher. This same sort of relationship is seen when changing the capacitance. As the capacitance gets larger, the difference between the discharge and time gets smaller until it flips, and the discharge becomes larger than the charge. This also goes back to what Callie was saying about the relationship between the offset knob and the voltage value. PI 2 : Do some research on the “RC circuit” in your textbook or online to learn more about 𝜏 . Do the results of your group’s analysis agree or disagree with this published result? Make sure you explicitly discuss the graphs generated for DA 1. Comment on any systematic errors that might be present in your data. Make sure you cite the source(s) you use.

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