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This applet is an electrostatics demonstration which displays the electric field in a number of situations. You can select from a number of fields and see how particles move in the field if it is treated as either a velocity field (where the particles move along the field lines) or an actual force field (where the particles move as if they were charged particles). This helps you visualize the field.

When you start the applet, you will see 500 particles moving in a point charge field. By default the particles are treating the field as a velocity field, which means that the field vectors determine how fast the particles are moving and in what direction. In this case, the particles just move toward the center. The velocity of all the particles at a certain point on the grid is always the same. If the field is a force field, then the field vectors determine the acceleration of the particles, but their velocity may vary depending on where they started.

The Field Selection popup will allow you to select a vector field. The choices are:

The Display popup will allow you to select how the field is displayed:

The Mouse popup controls what happens when you click on the box. If you set it to Adjust Angle or Adjust Zoom, you can adjust the orientation or size of the 3-d view by clicking and dragging on the box.

The Slice popup allows you to look at planar slices of the box rather than looking at the contents of the entire box. If the popup is set to No Slicing, you view the entire box. Otherwise you will see the box sliced in one of three directions. The location of the slice can be adjusted by dragging the line running along the sides of box near the slice.

The Stopped checkbox will stop the particles.

The Reverse checkbox will reverse the direction of all the field vectors.

The Reset button can be used to reset the positions of all the particles to random values.

The Kick button can be used to give all the particles a random acceleration in some direction. This is only allowed if the particle movement is set to "Force". It can be useful if none of the particles are moving, or if they are all moving in the same direction.

The Field Strength slider makes the field stronger or weaker, and also adjusts the brightness of the field vectors if you have Display: Field Vectors selected.

The Vector Density slider controls the number of vectors present if you have Display: Field Vectors selected.

The Number of Particles slider allows you to reduce the number of particles, which can be useful if you want to watch the behavior of just a few of them. Also it might speed things up if you have fewer particles.

A few additional field-specific sliders may be present, depending on the field you have selected.

Click here to go to the applet.