Lab 4

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Rio Salado Community College *

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112

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Electrical Engineering

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Apr 3, 2024

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PHY112 Lab 4 Name Michaela Blackmore Capacitors Access the PhET Capacitor Lab Simulation . Click the Play button and select the option to “Run CheerpJ Browser-Compatible Version”. Use the simulation to answer all the following questions. Part 1 – Capacitance 1. Check the boxes marked plate charge and voltmeter. Move the red voltmeter lead so that it touches the top plate, and move the black voltmeter lead so that it touches the bottom plate. Your simulation should look something like this: 2. Move the slider on the battery up to change the voltage between the capacitor plates. The voltage between the plates will match the voltage of the battery. Record the

voltage and the resulting stored charge. Measure six different values and complete the data table below: 3. Use Excel, another spreadsheet, or a graphing program to create a scatter plot graph of voltage versus charge data. Graph the voltage on the horizontal axis and the stored charge on the vertical axis. Make sure that your graph has an appropriate title and that you properly label both axis. Apply a linear fit to your graph and include the equation. Copy and paste your graph below Voltage ( V ) Stored Charge ( C ) 1.5 1.33 *10^-13 1.0 0.90 *10^-13 0.7 0.63 *10^-13 0.5 0.46*10^-13 0.2 0.18*10^-13 0 0

4. Check the capacitance box on your simulation. How does the capacitance compare to the slope of your graph? What is the physical meaning or the significance of the graph slope? 5. If the voltage applied by the battery doubles, what happens to the amount of charge stored on the plates and the capacitance of the capacitor? 6. If you double the plate area, by what factor does the capacitance change? Explain the reason for this change. Don’t explain the math but explain the theory behind the math. The capacitance box value is equal to 0.89 *10^-13F and does not change when voltage of the battery is manipulated. The slope of the graph is 0.855*10^-13. These values are approximately equal which means the slope represents the capacitance of the simulation. The graph shows charge over voltage which is the how capacitance is calculated. If the voltage by the battery doubles then the amount of charge stored on the plates will also double since the relationship is directly proportional. The capacitance of the capacitor will remain the same despite change in voltage. When the plate area is doubled the capacitance doubles as well. This is because there is more area.The greater the area of the plate the more room there is and the less likely for repulsions of like charges. This allows more charge to be held on the plate.

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7. Reduce the plate separation distance by half (move the plates closer together). By what factor does the capacitance change? Explain the reason for this change. Don’t explain the math but explain the theory behind the math. Part 2 – General Observations and Analysis 8. Reset the simulation. Check all the boxes. Move the voltmeter leads so that the red lead touches the top plate and the black lead touches the bottom. Place the field meter in the space between the plates. Increase the battery voltage to 1.5. Your screen should now look something like the picture below. Decrease the plate separation distance. Note the effects of this change on the - stored charge, - stored energy, and If the separation distance is decreased by 1/2 the the capacitance doubles in value. This is because when the plates are closer the electrostatic field force is stronger.

- voltage (note that you will need to adjust the voltmeter leads as you move the plates, and the leads need to be in contact with the plates to get a proper reading). Record your observations on the data table below. Explain why each of the changes occurs. Remember that math describes WHAT happens but does not explain WHY – you may use math to aid your discussion, but your explanations should focus on what is happening in the system. You may need to review the lesson to help you in this section. For three different separation values, measure the voltage across the plates using the voltmeter. Then calculate the Electric field strength ( ). Record the data and calculations. Following your calculations, what do you observe about the Electric field strength as the capacitor plates move closer (with the battery connected). Observed value Observed change as capacitor plates move closer Explanation for the change (battery connected) Stored charge ( C ) Doubled The stored charge is doubled when the plates move closer. This is because the plates are more attracted when closer in proximity which decreases repulsion and allows stored charge to increase. Stored energy ( J ) Doubled Stored energy will double when the plates move closer. This is because there is more charge available and because the amount of work required is decreased as the plates attract each other. It takes more effort to separate plates. Voltage ( V ) No change Voltage is the constant being observed.It is not affected by the change of charge, energy, or distance of the plates. Unless changed, the battery is still supplying the same voltage selected. E = Voltage separation = V d Voltage (v) Separation (m) Electric field strength (V/m) 1.5 0.01 150 1.5 0.0075 200 1.5 0.005 300 Observed value Calculated change as capacitor plates move closer Explanation for the change (battery connected)

9. Reset the simulation back to its default settings. As before, check all the boxes and move the voltmeter and field meter into position. Slide the battery to the 1.5 V position, and then click on the disconnect battery button . Decrease the plate separation distance. Note the effects of this change on the - stored charge, - stored energy, and - voltage (note that you will need to adjust the voltmeter leads as you move the plates, and the leads need to be in contact with the plates to get a proper reading). Record your observations on the data table below. Explain why each of the changes occurs; however, you may need to revisit the textbook or lesson discussion to help with the explanation section of the table. For three different separation values, measure the voltage across the plates using the voltmeter. Then calculate the Electric field strength ( ). Record the data and calculations. Electric field strength (V/m) Increases The electric field strength increases as the capacitor plates move closer. This is because the opposite charges become more attracted the closer the get. Observed value Observed change as capacitor plates move closer Explanation for the change (battery NOT connected) Stored charge ( C ) Constant The stored charge will remain constant since it is isolated from the battery supply. The charges have no where to go when disconnected so it remains the same. Stored energy ( J ) Decrease The stored energy will decrease because there is no change in stored charge. As the distance decreases it has less energy since the plates are closer and want to attract. Voltage ( V ) Decrease The voltage decreases as the plates move closer because the battery is no longer hooked up providing a constant V in the system. E = Voltage separation = V d Voltage (v) Separation (m) Electric field strength (V/m) 1.5 0.01 150 1.14 0.0075 152

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Following your calculations, what do you observe about the Electric field strength as the capacitor plates move closer (with the battery NOT connected). Part 3 – Series and Parallel 10. Click on the multiple capacitor tab at the top of the simulation. Check the box for the total capacitance meter. Increase the number of capacitors in series and note the effect on the total capacitance. Describe your observations and provide an explanation for this behavior. 11. Increase the number of capacitors in parallel and note the effect on the total capacitance. Describe your observations and provide an explanation for this behavior. 0.75 0.005 150 Observed value Calculated change as capacitor plates move closer Explanation for the change (battery NOT connected) Electric field strength (V/m) Constant The electric field strength remains the same since there is no constant voltage provided by the battery which decreases the total electric field strength. Since distance is decreasing then the voltage generated without the battery is proportionally decreasing. As the capacitors increased in number the total capacitance meter decreased with each addition in series. This is due to resistance between the plates since they are stacked. The charges are pushing off the bottom plates onto the top plates of the next circuit which causes equal amounts of charge to leave the bottom plates. As more capacitors are added then the overall separation distance increases resulting in lower capacitance in the series. As the number of capacitors increase in parallel, the total capacitance increases. This is because the plates are parallel to each other which decreases the resistance between the plates. This increases surface area which results in overall total capacitance since charge can be spread out between the circuits.

Part 4 – Final Conclusions and Summary Give a concise summary of the findings for this lab. What do you understand now that you did not understand before? Be specific. Capacitance is the ability of a system to store electric charge. This lab allowed me to investigate the relationships between the variables that determine capacitance which included area of the plates and separation between the plates. It also allowed me to observed the relationship between capacitance, the charge on the capacitor plates, and the voltage across the plates along with capacitance of capacitors placed in series and in parallel.These are all concepts that have been made clearer to me while interacting with the lab. The capacitance does not change when voltage of the battery is manipulated. The slope of the graph is 0.855*10^-13 in the first simulation and this represented how charge is related to voltage which is the how the capacitance is calculated. The capacitance of the capacitor will remain the same despite change in voltage. plate area is doubled the capacitance doubles as well. This is because there is more area.The greater the area of the plate the more room there is and the less likely for repulsions of like charges. This allows more charge to be held on the plate. However is the separation distance is decreased by 1/2 the the capacitance doubles in value. This is because when the plates are closer the electrostatic field force is stronger. The lab simulation allowed me to physically see charges created by the manipulation of variables. Although the relationships between each variable is understood by equations, this allowed me to understand the concept. In part two, additional variables were created. It was observed with a battery connected and without a battery connected. When the battery was connected to the circuit, it was observed that the stored energy and stored charges increased by double. This is because the addition of the voltage of the battery and because the plates are more attracted when closer in proximity which decreases repulsion and allows stored charge to increase. When the battery was removed then the stored energy and voltage both decreased. This is because as the plates move closer because the battery is no longer hooked up providing a constant V in the system which allows for decrease in charge resulting in less energy. The electric field strengths were then calculated. The electric field strength remains the same since there is no constant voltage provided by the battery which decreases the total electric field strength. Since distance is decreasing then the voltage generated without the battery is proportionally decreasing. Next, capacitors were observed in a series and a parallel form. When in a series, the charges are pushing off the bottom plates onto the top plates of the next circuit which causes equal amounts of charge to leave the bottom plates. As more capacitors are added then the overall separation distance increases resulting in lower capacitance in the series. When parallel, the increased surface area results in overall total capacitance since charge can be spread out between the circuits.

Lab 4

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