Physics 42 Lab: Capacitance and Dielectrics

[Pages:2]Physics 42 Lab: Capacitance and Dielectrics

The purpose of the lab is to explore the properties of a parallel plate capacitor with and without a dielectric. We will test the theoretical prediction for the capacitance of a capacitor and how capacitance depends upon plate separation distance.

For a parallel plate capacitor with surface area A, plate separation distance d, dielectric constant , the capacitance, C is predicted to be:

C 0 A d

where the permittivity of free space is given as: 0 8.85x1012C2 / Nm2

Equipment: 2 Parallel Plate Capacitors, 1 Multimeter, 4 alligator clip cables, 2 wires for measuring capacitance, various sheets of dielectric materials, 1 clear plastic ruler

Part 1: Capacitance vs. Plate Separation

Set up the capacitor with the multi-meter as shown by your instructor. Make a data table in excel being sure to label everything including units on the measurements. Measure the diameter of the capacitor. Measure the capacitance for at least 10 separation distances, starting at 1.00 cm. Calculate the capacitance using the theoretical equation for each of these distances assuming the dielectric constant for air is 1.00059. Put the calculated values in a column next to the measured values. Calculate the percent difference between theory and experiment for each measurement, and find the average error for all measurements. Plot capacitance vs plate separation distance. Analyze the graph using an appropriate fit and discuss your results. Does your result agree with the theoretical prediction?

Part 2: Capacitance with Dielectrics

Select three different dielectric materials to test. You need to find a plate separation distance that you can hold constant for the different materials, in order to compare the capacitance, so play around with the materials and find a distance that will work. It will not be exact but try to get the distances as close to each other so you can do a qualitative comparison. Put the distances in a table for each material along with the measured capacitance. From the capacitance equation, calculate the dielectric constant for each material. Go online and find a website that lists the constants. What materials have dielectric constants closest to watch you found? Make sure you include the website URL and the name and dielectric constant values you found online. Get a percent difference between what you found online and what you measured. Briefly discuss your results and how the different materials compared.

Part 3: Capacitance in Parallel and in Series.

Set the plate separations for two capacitors and calculate and measure the individual capacitance of each capacitor alone. Calculate the predicted equivalent capacitance for the two in parallel and in series using the following relationships.

Capacitors in Parallel: V V1 V2 Ceq C1 C2

Capacitors in Series: V V1 V2

1 11

Ceq C1 C2

Show your calculations. Hook up the capacitors in parallel and in series and measure the total capacitance of the system. Use a second multimeter to measure the voltages across each capacitor and the total voltage of the system. Calculate the percent differences between your calculated and measured results and put all the data in your data sheet. Briefly discuss your results.

Your lab report should include a brief abstract at the start of your report which summarizes results.

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download