PHY 2049L
Lab 1

Equipotentials and Electric Fields

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Updated: 1/21/2013
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Guiding Question:

Note: For this lab, there is both a quantitative and a qualitative answer to the guiding question.

Preparing for the lab:

We will be doing a VARIATION of "Lab 26", which starts on page 259 of the lab manual. The differences are described in a handout.

Read the theory for "Lab 26" (pages 259 and 260 in the lab manual) and then answer the pre-lab questions on LON-CAPA.

Comments

There are significant differences between what we will do and what is described in the lab manual procedures. We will only do two cases (see picture below) but will make some additional measurements so we can answer quantitative questions similar to those asked about the omitted case. The procedure handout should be available the week before you do this lab. If not, you will have it at the start of the lab. You will also get a handout containing the data tables for our measurments and pages to use when drawing the equal potential lines and sketching the electric fields.


Setup

This picture shows the equipment pretty much as you will use it when measuring the potentials for the parallel plate capacitor (the first case we will do). The lab station should look this way when you arrive AND when you leave, so it is ready for the next group. This is set so the high (+5 V) potential is on the left and the low (0 V) potential is on the right, so the E fields will point downhill to the right. If you find that the location of the ground contact gets in your way, you can rotate the apparatus by 45 deg or so to make it easier to work with.

voltmeter, conductive paper sheets, power supply


Important details: Notice that the grid numbers are oriented so the x-y coordinate system reads from right to left and bottom to top. That is, x reads from low voltage to high voltage. This leads to a data table with a simple organization if you record the Delta-E pairs from left (high) to right (low) in parts 2 and 4 of the experiment. Be sure you set up the second sheet this same way. The black (grd/com) connection from the power supply and the black (LO) connection from the multimeter both go to the bottom end of the capacitor, the end we will call ground (0 volts). The red (+) connection from the power supply goes to the top of the capacitor, the end we will set at 5 volts. You check this with the red (+) probe from the multimeter, which needs to be set on the "20" range for DC Volts. Notice that the multimeter will use a probe for both of its connections to the conductive paper.

There is a separate page showing a closeup of the power supply so you can see the wiring (red from "+" and black from "com/gnd" and learn the controls we will use on it. It also shows a closeup of the multimeter in DC volts mode. We will use one or both of these instruments for half of the labs this semester, so become familiar with them.

 
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