E-Field

By Adam Cornett

Revised Wednesday, December 18, 2005

• This program is licensed under the GPL (GNU GENERAL PUBLIC LICENSE), a copy of which is included with this program in the file gpl.txt. Please read the license before changing or redistributing this program.
• This program is distributed without cost and without warranty.
• Requires Java© Runtime Environment 1.5 (also called Version 5.0) or greater. see http://www.java.com to download the JRE
• Execution Instructions:
  • Make sure the Java Runtime Environment is installed
  • Run the execuateable jar `E-Field.[version].jar`

How-To:

• Add Charges

  There are four ways to add a point charge to the simulation:

  1. Right click on the display where you would like the charge to be and click Add Point Charge. A window will popup for you to enter the electric charge and confirm the location.
  2. Click the Add Button in the upper right hand corner.
  3. Press Ctl-A.
  4. In the Actions menu, click Add...

     When entering the charge, you can use scientific notation in the following form: 0.00001 = 1e-5

• Edit Charges

  To select a charge, click on the charge in the simulation window, or select in in the list of charges. When a charge is selected, a while circle will be drawn around it.

  To move a charge, select it, click on it in the window and drag it to the desired location. The location can also be changed in the Edit Charge window.

  To edit a charge, select the charge, then either right click on it and click Edit.... In the edit window, you can change all of the properties of the charge. When changing the location, the units are pixels, not meters, so if the meters per pixel is not set to one(1) [see how-to section on changing options] then you will need to convert. While editing, you can use the drop down box at the bottom to change which charge you are editing, however if you change which charge without clicking Apply, the changes will not be saved.

• Changing the Display

  There are two different sets of lines that can be displayed, they are turned on and of by the check boxes in the lower right corner.

  • Field Lines:

    In this mode, Field lines are drawn from all positive charges. To change the number of lines drawn per charge, increase or decrease the number in the textbox in the lower left hand corner. The color of the line indicates the force of the field at that point.

  • Potential Lines:

    In this mode, potential lines are drawn over the field lines. The lines are all evenly spaced according to the electric potential, to set the spacing, see the set options section. The resolution of the lines is set by the center box below the simulation screen. The resolution determines the size of the pixel blocks that are used. If the resolution is set at 1, ever pixel will be looked at individually, if it is set at 2, then the potential lines will be drawn in 2x2 blocks. The higher the resolution, the lower the time it takes to draw (1/(n*n)). The time is also dependent on the size of your screen and the number of charges.

• Changing Options

  This program has several options, most of which are self-explanatory, however some do need some explanation.

  To get to the options window, press Ctl-o or Options... in the File menu.

  Gradient Min/Max: These values set the minimum and maximum force values for the gradient of the field lines.

  Potential Spacing: This value sets the spacing (in volts) between the potential lines.

  Potential Offset: This value sets the minimum potential value, for drawing potential lines.

• Loading/Saving Data

  The program data (charges and options) are saved to disk every time the program exits in the file state.o. If you wish to save the data else where where it will not be overwritten, use File->Save... to open the save file window. Save the file, it does not automatically the file extension, so be sure it is in the filename (.o).

  The program automatically loads the last data file state.o when it starts up. To load another data file, use File->Load... However, you must be careful because the program will try to open whatever file you select, so make sure you choose a .o file to load, if the file does not load, it may be corrupt or an incorrect version. To view the error log, see Log.# where # is a number, the highest number is the most recent log file.