Electric Fields and Electric Potentials

PY 212 Section 219Vellie Johnson

TA: Craig HufferJanuary 26, 2009

I. Introductiona. Objectives:

The objective of this lab was to explain the interaction of particles or bodies through space, the action-at-a-distance force between two bodies that are not in physical contact. The gravitational field gets weaker as you fo farther away from the source. An electron modifies the space around it in such a way that other particles with the same charge are repelled, while particles with the opposite charge are attracted. The same way a mass in a gravitational field has PE, so does a charge in an electric field. The aspects of the electric field and the electric potential will be recorded by examining the nature of electric fields by mapping the equipotential lines and then sketching the electric field lines.

II. Theory:i. The charged body that is place in an electric field (E)

experiences a force (F). The magnitude of the force is divided by the maglitude of the charge (q) on the body.

The force on an electron always points toward the electron from all directions, since that is the way that a positively charged body would move.

ii. Work (W) is done by moving a charged object through an electric field which is given by

W=Fd=qEdiii. The negative of the work done by the electic force is defined as

the difference in the potential energies (∆U) which can be found by

-W=∆U=(Ufinal-Uinitial)iv. The work done by the electric field is

W=-q∆V; where∆V=Vfinal-Vinital is the potential difference.

The electrostatic potential (V) is defined as the electric potential energy of the body divided by its charge: V=U/q.

III. Results and DataPlease see attached graphs for the data from the three different

graphs.IV. Analysis

The graph drawings of equipotential lines and electric field lines showed that like charges try to get as far away from each other as possible and that electrical charge always goes from positive to negative. When you look at the equipotential lines you can see that there is a correlation between the distance between the two electrodes 5+ and 0 and the equipotential lines have the same ratio of distance between the 5Volt bolt and the 0Volt bolt electrical field lines no matter where they originate and terminate. The charge of the

electrical field was determined by measuring the charge at certain points on the paper using an electrode.

The graphs also show that the electrical field lines extend all the way from one end of the paper to the other end of the paper and charges try to get as far away from each other as possible. This can be seen when you compare the location of charges.

V. Discussiona. General Conclusions

The graphs show very accurately the charges that are locatedthroughout the paper due to equipotential and electrical fieldlines.

b. Discussion of Error and AssumptionsThe lab proved to be very accurate when the electrodes were

working correctly. There could have been more electrical field readings taken to show that equipotential lines are not going to cross. There seemed to be a higher charge on the end of the electrode connection where the bolt was and the charge seemed to get lower as the distance along the lead line got further away from the bolt.

c. Answers to questions posed in the lab manualOn the “parallel lines” graph you can see that charges that are

outside of the parallel lines try to get as far away from each other when they get towards the end of the paper. Nowhere on the paper do you see a position where the electrical field lines or the equipotential lines ever cross. All elecrical field lines are places wehre the electrical charge is the same. When connecting like charges together you never get an overlap of electrical fields. Equipotential lines are lines that extend from the 5Volt probe and terminate at the 0Volt bolt. Equipotential lines extend through each electrical field line at a 90˚ angle and never cross either. To make sure this is the case we could have done more electrical field lines and seen if we had any equipotential lines that crossed, FYI you wouldn’t!

There are a few situations where this could be a representation of a situation. Take a positively charged magnet and place it down on the table and then take another positively charged substance (dust) and place that down on the table next to the magnet. You will see the dust reallocate itself away from the magnet depending on the amount of repelling force enduced on the dust by the magnet.