Electric Field and Potential: A Physics Lab Report

Report N° 2: Physics Laboratory II

Electric Field and Potential

Concepción, April 13, 2009

Members:

• Carla Cáceres
• Jorge Gonzalez
• Fabián Soto

Teacher:

• Alberto Inostroza

Assistant:

• Raul Augurto

Objectives

• Determine how to map electric potential in a plane and draw equipotential lines.
• Derive the form of the electric field charge distribution in the plane from the equipotential lines diagram.

Materials

• Graph paper
• Glass cuvette
• Cables
• Voltmeter
• Multimeter
• Water
• Support

Setup

After verifying the materials were in good condition, the work platform was assembled. The glass cuvette was filled with approximately 3-4 mm of water. A sheet of graph paper was placed beneath the cuvette, aligned so that the gridlines were straight. Using the support, the positive and negative leads of the voltmeter and multimeter were connected. Millivolt measurements were taken as the probes were placed in the water, at various points near the positive and negative sources. The values were recorded in a table for report preparation.

Theoretical Introduction

Key concepts for this report:

Equipotential Surfaces:

Areas where the electric potential is the same at every point.

Power Lines:

Lines used to visualize the electric field strength, with higher density indicating greater intensity (lines run from positive to negative).

Electric Field:

A disturbance created by an electric charge in its vicinity.

This lab demonstrates the existence of the electric field and explores how to map the lines of force and their direction.

Scenario Approach

• An electric field is present.
• Power lines run from positive to negative.
• The water acts as an equipotential surface.

Measurements

Table of Measurement Data Obtained

(x, y) millivolts (x, y) millivolts (x, y) millivolts (x, y) millivolts
(0,0) 4.55 (4,0) 2.65
(0,1) 4.57 (5,0) 2.20
(0,2) 4.58 (6,0) 2.41
(0,3) 4.60 (7,0) 2.61
(0,4) 4.62 (8,0) 2.81
(0,5) 4.64 (1,1) (1.7,8.4)
(0,6) 4.65 (2,2) (2,3)
(0,7) 4.66 (3,3) (2.4,2.3)
(1,0) 4.26 (4,4) (3.2,2)
(2,0) 3.88 (5,5) (5.4,6.8)
(3,0) 3.32 (1,1) (1.7,8.4)

Analysis

1. Assemble the system for the charge distribution assigned by the teacher: dipole, parallel plate, flat plate, or point charge.
2. Pour water into the glass cuvette to a depth of approximately 3-4 mm.
3. Measure the electric potential between the negative electrode and each grid point on a horizontal plane.
4. Tabulate the data, including the position (x, y) and the potential value. Use this data to draw the equipotential lines.

(x, y) millivolts (x, y) millivolts (x, y) millivolts (x, y) millivolts
(0,0) 4.55 (4,0) 2.65
(0,1) 4.57 (5,0) 2.20
(0,2) 4.58 (6,0) 2.41
(0,3) 4.60 (7,0) 2.61
(0,4) 4.62 (8,0) 2.81
(0,5) 4.64 (1,1) (1.7,8.4)
(0,6) 4.65 (2,2) (2,3)
(0,7) 4.66 (3,3) (2.4,2.3)
(1,0) 4.26 (4,4) (3.2,2)
(2,0) 3.88 (5,5) (5.4,6.8)
(3,0) 3.32 (1,1) (1.7,8.4)

On the diagram, draw vectors representing the electric field directions in the plane. Compare the results with the theoretical description for the corresponding symmetry.

Given the results, determine the functional relationship between potential and distance. For cylindrical electrodes, correct the curve (take ln r).

Conclusions

• Using the lab data, a diagram of equipotential surfaces and lines of force was constructed, providing a visual representation of the electric field.
• The electric potential equation was determined to be Y = -1.72X + 5.06. Differentiating with respect to x gives dy = -1.72, resulting in an electric field of E = 1.72.

Comments

As this was our first laboratory experience, completing this report was challenging (conducting the measurements was also more complex due to our initial unfamiliarity with the procedures).

References

• Serway, R. (1996). Physics Volume 2. Mc Graw Hill.