lab

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 1/8

UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment

Assignment # 2B Name Lab 2 Experiment I worked in a group with

Evan Hathaway - Jun 30, 2020, 11:32 AM CDT

Update and Submit

Equipment

Content LA Thirteen - Jun 10, 2020, 8:33 PM CDT

1 Field Mapper Kit PK-9023

Replacement Supplies:

Conductive Ink Pen PK-9031B

Conductive Paper w grid PK-9025

Conductive Paper (no grid) PK-9026

1 Short Patch Cords SE-7123

1 Digital Multimeter EX 330

1 DC Power Supply TP3005T

Content LA Thirteen - Jun 10, 2020, 8:36 PM CDT

Setup

Content LA Thirteen - Jun 10, 2020, 8:36 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 2/8

Figure 2: Setup

Figure 3: Patterns

1. Prepare the patterns in Figure 3 using the conductive pen and conductive paper. The patterns must dry completely before use. The letters are for reference only and should not be drawn on the paper. The + and – are to show where to connect the electrodes and should not be drawn on the paper. The circles in patterns C are free floating and should not be connected to the power supply.

2. Attach the conductive paper with the pattern on it to the cork board with push pins at the four corners. The paper is not very conductive, but must carry a little current for the voltage sensor to work. The fact that the paper carries a small current actually affects the electric field somewhat and near the edges of the paper the effects may be noticeable.

Content LA Thirteen - Jun 10, 2020, 8:58 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 3/8

3. Insert the push pins into the appropriate electrodes on the pattern drawn on the conductive paper. It is important that you do not bump the electrode push pins during the experiment since doing so may change the voltages on the paper. This is not a disaster since the shapes of the equipotential surfaces will not be affected, but it is frustrating to be tracing a 4.0 V surface that suddenly becomes a 3.0 V surface.

4. Connect the DC power supply’s output (plus and minus) to the silver push pins using the banana plug cables and alligator clip (See Figure 2).

5. Turn the DC Power supply on. Using the DC regulated power supply, set the voltage to 15.00 V. To do so, press the voltage knob (push several times to change which digit is being adjusted), and rotate the knob so the display reads 15.00 V. At this stage, the current should read 0.000 A.

6. Set the current to about 0.001 A, such that the voltage reaches 10 volts and remains stable. You may notice that the current decreases to zero.

7. Attach the ground lead of the Digital Multimeter to the ground terminal of the DC Power supply. You now have one free lead of the DMM to be used momentarily.

Procedure A: Plotting Equipotential Lines

Content LA Thirteen - Jun 10, 2020, 8:46 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 4/8

1. Turn on the DMM to DC Voltage measurement mode.

2. Check for good connections by first touching the red lead of the voltage sensor to the paper near (not touching) the negative electrode. The voltage reading should be 2-3 V. The value near the positive electrode should be at least 6 V. For the conductors drawn, make sure the voltage is the same everywhere on the circle or line, however, when doing so apply minimal pressure to the conductors, as the DMM probes can be a little sharp and may puncture the silver. If not, there are breaks in the line. Get a new pattern.

3. Draw your pattern onto the white grid paper to scale.

4. Trace the 4.0 V equipotential. To do this, locate a place on the paper near the positive electrode where the voltage is 4.0 V. Try to keep the probe at the same angle (Figure 4) and use the same pressure for each reading (the voltage is pressure sensitive). Record the point on your white grid paper and write 4 V next to it. Hint: near a point electrode, the 4.0 V equipotential should be roughly circular. For other electrodes, the 4.0 V equipotential should roughly be parallel to the electrode. Important: This experiment is not precise. 4.0 V will be within a few tenths of a volt. Do not waste time trying to find the exact spot! This process is meant to be quick.

5. Locate 5 more 4.0 V points to make an equipotential surface. Mark these points on the white grid paper.

6. This process will be repeated again with a different voltage to create another equipotential surface. Find 6 more equipotential surfaces by picking new voltages. Record the points onto the white grid paper and write the voltage next to each point.

7. Turn off the output of the signal generator (not the signal generator itself).

Figure 4: Probe Position

8. Connect the points that are at the same voltage. Draw smooth curves if they don’t go exactly through each data point (Figure 5). Everything on this line is an equipotential surface.

Figure 5: Equipotential Surfaces

Content LA Thirteen - Jun 10, 2020, 8:56 PM CDT

Procedure B: Plotting Electric Field Lines

Content LA Thirteen - Jun 10, 2020, 8:58 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 5/8

1. Tape the two leads of the voltmeter together for this procedure (see Figure 7). The technique is to use the voltmeter leads to find the direction from an electrode that follows the path of greatest potential difference from point-to-point.

NOTE: Do not attempt to make measurements by placing the leads on the grid marks on the conductive paper. Touch the voltmeter leads only on the solid black areas of the paper. It may be necessary to use higher voltmeter sensitivity for this measurement than was used in measuring equipotentials

2. Reactivate the output of the DC power supply, again with 10 V DC.

3. Place the voltmeter ground lead near one of the dipoles to plot the field lines on the conductive paper.

4. Place the other voltmeter lead on the paper and note the voltmeter reading.

5. Pivot the lead to several new positions while keeping the ground lead stationary (see Figure 7).

6. Note the voltmeter readings as you touch the lead at each new spot on the paper.

7. Draw an arrow on the paper from the ground lead to the other lead (see Figure 8) when the potential is the highest,

8. Move the ground lead to the tip (head) of the arrow.

9. Repeat the action of pivoting and touching with the front lead until the potential reading in a given direction is highest.

10. Draw a new arrow.

11. Repeat the action of putting the ground lead at the tip (head) of each new arrow and finding the direction in which the potential difference is highest. Eventually, the arrows drawn in this manner will form a field line.

12. Return to the dipole and select a new point at which to place the voltmeter's ground lead.

13. Probe with the other lead until the direction of highest potential difference is found.

14. Draw an arrow from the ground lead to the other lead

15. Repeat the process until a new field line is drawn (see Figure 9).

16. Continue selecting new points and drawing field lines around the original dipole.

Figure 6: E Field Lines

Note: equipotential lines near the edge of the paper will be distorted. The system is not quite static since some current is required for the voltage sensor to function. The E field lines show the path that charge (current) follows. Current cannot flow from the conducting paper into the air, so the field lines must either run parallel to the edge or avoid it. Places to the left and right of the pattern show an almost constant voltage, so in these places the electric field must be nearly zero. At the top and bottom of the pattern, the E field lines run parallel to the edge and the equipotentials must be perpendicular to the edge. This modification of the field is produced by surface charge on the edge of the paper.

Content LA Thirteen - Jun 10, 2020, 9:08 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 6/8

Figure 7: E Field plot setup

Figure 8: Probe position showing highest potential

Figure 9: Example of three field lines between unlike dipoles

Analysis:

Content LA Thirteen - Jun 10, 2020, 9:08 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 7/8

Pattern A: Attractive Dipole 1. What is the relation between the direction of electric field and equipotential line at the same point? (A geometrical relation is desired.) 2. What effect does the finite size of the black paper have on the field? Pattern B: Parallel Plate Capacitor 1. What is the field outside the capacitor plates? 2. How does the ratio of the plate length (l) versus separation (d) affect the fringing effect at the edges of the plates? Pattern C: Floating Electrode 1. How does the circular electrode distort the field? 2. What is the potential of the circular electrode? Of the area inside the electrode? 3. What effect would moving the circular electrode have? Pattern D: Coaxial Cable 1. What is the field inside the inner conductor, between the two conductors, and outside the outer conductor?

Content LA Thirteen - Jun 10, 2020, 9:11 PM CDT

3/7/2021 UNT PHYS 2240 Lab SPRING 2021 - Alymjan Rejepov/Experiment 2: Electric Field Plotting/Experiment - LabArchives, Your Electronic La…

https://mynotebook.labarchives.com/entries/print_page/ODkwOTE2LjB8Njg1MzIwLzY4NTMyMC9Ob3RlYm9vay8yNjQyODEzODIwfDIyNjE1NTYuMA… 8/8

Conclusions:

Content LA Thirteen - Jun 10, 2020, 9:11 PM CDT

Discuss any interesting points about your pattern. As appropriate, answer each of the questions that follow. It is interesting to note that pattern A is the attractive dipole that show in most textbooks. Pattern B is a parallel plate capacitor, pattern C is a floating electrode between a parallel plate capacitor, and pattern D is a coaxial cable. 1. Draw the distribution of charge for the conductor(s) in your pattern. Remember that electric field lines begin on positive charges and terminate on negative charges. A higher field line density implies a larger charge, and a lower field line density implies a smaller charge. Write a + where each line begins and a – where each line terminates. 2. Does your pattern have the same symmetry as the charge distribution? 3. Do the field lines cross each other, should they cross? 4. Are the field lines perpendicular to the surface of your conductor? 5. Where in the pattern is the field strongest/weakest? Note that where the equipotential surfaces are close together, the electric field must be strong (why?) 6. Is there any evidence of charge polarization in your pattern?

Content LA Thirteen - Jun 10, 2020, 9:13 PM CDT