physic lab report

Electric Fields

Purpose:

In this lab we will create visual representation of electric fields in order to better understand them.

Introduction:

Electric fields cannot be observed directly or quantified with a single measurement. “Picturing” things in Physics is an important part of understanding them. Things often need to be studied by analogy because of the difficulties in making direct observations of them. In this experiment, we do both. We wish to develop a “picture” of the electric field in space. What we will observe is the passage of electricity through material and the voltage (or potential) differences this causes. This is analogous to the actual electric field.

Procedure:

For this lab, we will be using special paper that has been impregnated with carbon, which acts as a semiconductor, meaning it conducts electricity at a level between a wire (conductor) and an insulator. The paper has a grid laid out on one side to facilitate transferring locations from the semiconductor paper to a sheet of graph paper where you will produce the drawings of your electric fields.

The paper is placed on a board and then two electrodes (metal conductors held at different voltages) are put on the paper with special ink. The electrodes are held at a potential difference by batteries (~3V). On a separate sheet of graph paper, draw the two electrodes to scale in the same location as on your semiconductor paper.

To trace the electric field, we must first find equi-potential lines. These are a series of points that have the same electrical potential. Points on the carbon impregnated paper that are at equal voltage potentials can be located using a voltmeter in either of two methods or a combination of both:

Place one probe of the voltmeter on one of the electrodes and measure the voltage difference to a point on the paper. Mark that point on a separate sheet of graph paper. Moving the probe around on the paper, find other points that have the same potential as the first, and mark them on your paper as well.

Place one probe of your voltmeter on the semiconductor paper to use as a reference. Move the other probe around the paper to find additional points that have zero potential difference from the reference.

Once you have found a number of points, all at the same potential and plotted them on your graph paper, connect them lightly in pencil. This is an equi-potential line. Several of these equi-potential lines plotted on your graph paper will enable you to sketch the electric field lines.

On your sheet of graph paper with the electrodes reproduced, plot the sets of equi-potential points and smoothly connect each set to form equi-potential lines. Then sketch the electric field lines. They go smoothly from one electrode to the other crossing the equi-potential lines at right angles always . This completes the picture of the electric field for a particular set of electrodes.

Do this for two standard sets of electrodes (pictured) and another of your own making or choosing.

Analysis:

Turn in your electric field diagrams with your lab report. (No calculations required!) Make observations on the shapes of your electric fields based on the shapes and placement of your electrodes.

Lab Evaluation:

Please provide feedback on the following areas, comparing this lab to your previous labs: How much fun you had completing this lab; How well the lab prep period explained this lab; The amount of work required compared to the time allotted; Your understanding of this lab; The difficulty of this lab; How well this lab tied in with the lecture. Please assign each of the listed categories with a value from 1-5, with 5 being the best, 1 the worst. Comments supporting or elaborating on your assessment can also be very helpful in improving the future labs.

Fluke DVM

Probes

Semi-conductor paper

Electrodes

Equi-potential lines

Electric Field lines

Electrode

Electrode