Lab Activity: Capacitor Lab

If you are taking this course through PA Homeschoolers, you must submit this lab report.

     There are two parts to this activity. In the first part, you will build three capacitors and investigate the affect of plate size and plate separation. In the second part, you will use a simulation to make further investigations about the behavior of a capacitor. Both parts have the same goal: To investigate the nature of electrical capacitance.

Part 1:

     In this part of the activity, you will build several capacitors and investigate some of their properties. 

Materials needed:

• Aluminum foil
• Magazine paper
• Masking tape
• Copper wire
• Digital multimeter that can measure capacitance

     The pictures below show how to construct a capacitor using aluminum foil, magazine paper, and masking tape. If you don't have magazine paper (it's coated with plastic), then you can use writing paper. Use these materials to build three different capacitors with different lengths of foil. Don't make the length smaller than 4 inches for any of the capacitors. Use your digital multimeter to measure the capacitance of each one. Your multimeter must be in capacitance mode to make these measurements. Note that the reading will be shown in nanaofarads.

     Based on the data that you collect, answer the questions shown below in the analysis section of the lab report. Provide an explanation for your answers in the conclusion.

One of the plates with the copper wire lead attached to the upper right part of the plate with tape.

A second plate/paper combination is placed on top of first plate. Note how the copper lead is attached on lower left rather than upper right part of the second plate.

A third sheet of paper is placed on top of the stack.

Now use a pen to help roll the capacitor into a tube.

Tape the tube in several places so that it doesn't unroll. Make sure that you tape the top and bottom of the tube. 

Make sure to have your multimeter in capacitor mode, as shown above. The reading will be in nanofarads when you connect the leads of the multimeter across the capacitor.

Question 1: Does the size of the aluminum foil in your capacitors affect the capacitance? 

Question 2: Create a graph of capacitance vs. plate area for your three capacitors. Determine the slope of the graph. Use the slope to determine the distance between the plates of your capacitors.

Question 3: A typical piece of copy paper has a thickness of 0.0004 inches. Convert this to meters and compare it to the distance you calculated in Q2. Explain any difference you find.

Question 4: If you squeeze the capacitors (by pinching them as you take a reading) does the capacitance change? Does the amount you squeeze make a difference? What does this tell you about the width of the paper? Does that width completely fill in the space between the plates? Explain you response.

Part 2: 

     In the second part of this activity you will investigate the relationships between the important parameters that effect the capacitance of a parallel plate capacitor. Begin by making adjustments to the "introduction" activity:

• Charge the capacitor by adjusting the battery voltage.
• Click the box to view the field lines.
• Notice how the direction of the field is based on the polarity of the battery.
• Use the voltmeter to measure the voltage across the plates.
• Change the plate area.
• Change the plate separation

     Draw a sketch of the set-up in your lab notebook. Use the other meters to help answer the following questions and record the data you collect in the analysis section of the lab report nd then record your answers in the conclusion section.

1. Use the capacitance meter to view the capacitance of the device. Which of the controllable parameters effect the capacitance?
2. Using the stored energy meter, determine which of the controllable parameters effect the stored energy.
3. Using the plate charge meter, determine which of the controllable parameters effect the plate charge.
4. Set the battery voltage to +1.5 volts, the plate separation to 5.0 mm, and the plate area to 100.0 mm². Calculate the capacitance, plate charge, and stored energy (use the energy equation U = (1/2)CV² which you will learn about in the next presentation) to verify that the values match those shown on the meters.

     Now switch the simulation to the lightbulb experiment. Use the battery to charge the capacitor and then the switches to discharge it through the lighbulb. Perform this discharge experiment several times, each time with the same battery voltage but a different plate separation. What do you notice about the discharge cycle time when the plate separation is different? Provide an explanation for your findings.