Monday, September 23, 2013

2D Charge Particles Model by Wolfgang Christian

this is a remixed of Point Charge Electric Field Demo Model written by Wolfgang Christian.
2D Charge Particles Model by Wolfgang Christian
author: Wolfgang Christian and this version slightly edited by lookang

changes made:
  1. redesign the panel for control to be bottom
  2. added more options to the menu for ease of use
  3. made the drawing of charges proportional to the charges
  4. made the collision detection to pause when the test charge is inside the charges
  5. added evolution page to reflect the physics of motion
  6. added test mass, m = 1 kg
  7. added trail to show path of test charge that can be drag away and it will start from vx=vy=0

text taken from

Point Charge Electric Field Demo

The Point Charge Electric Field Demo model shows the electric field with multiple point charge configurations and vector field visualizations. Users can select these configurations from a drop down menu or can create their own configurations.

The electric field is defined as the force per unit charge that would be experienced by a very small test charge at a given location. The Point Charge Electric Field Demo model shows an ideal test charge with an arrow that represents the field at the test location. The numerical field magnitude is shown in a text-box near the bottom of the view as the test charge is dragged.

Because the electric field changes dramatically in the vicinity of a charged particle, it is difficult to visualize its global properties using only a single test charge. A good way to visualize the field's geometric structure is to use a test-charge grid. Test charges are placed uniformly and the force per unit charge is shown at each test charge location. Users can select the number of locations and can use either arrow length or brightness (gray-scale) to show the field's magnitude a the grid point.

Teaching Objectives

Forces, Energy and Fields

Attractive and repulsive interactions at a distance (e.g., gravitational, magnetic, electrical and electromagnetic) can be described and explained using a field model.

Learning Goal

Students understand that the field model explains how objects exert attractive and repulsive forces on each other at a distance: their fields are the agents of the interaction.

Essential Knowledge

The field of a source (e.g., a particle with charge) depends only on the properties of the source and the position of an object relative to the source, not on any properties of objects placed in the field (e.g., a test charge). The field of an object is always there, even if the object is not interacting with anything else.

The strength of the electric field at a certain location is given by the electric force per unit of charge experienced by a test object placed at that location. If the electrical field at a certain position is known, then the electrical force exerted by the sources of that field on any object at that position can be calculated by multiplying the field strength (E) and the charge of the object.


The Point Charge Electric Field Demo model was created by Wolfgang Christian using the Easy Java Simulations (EJS) modeling tool version 4.3.1. You can examine and modify the model for this simulation if you have EJS installed by right-clicking within the program and selecting "Open Ejs Model" from the pop-up menu.

Information about EJS is available at: <> and in the OSP ComPADRE collection <>.