Welcome to the Moving Charge Applet

This applet shows the field of a moving charge, and how it is concentrated directions perpendicular to the motion. It also shows how information only propogates at the speed of light, and shows how the accelerating charge emits radiation by the compression of electric field lines, which produces an electromagnetic wave.

  • Select Your Mode From the pull down menu and press go.
  • Use the scrollbar to accelerate the charge.

  • Modes:
  • Linear: the charge moves at constant velocity in the same direction.
  • Circular: the charge moves in a circle, experiencing centripetal accelaration.
  • Sine Wave: the charge moves in a path y = sin(t), x = t.
  • Saw Tooth Wave: the charge moves in a "saw tooth" path. Best at lower velocities.
  • Inward Spiral: the charge circles more tightly about a point. Best at lower velocities.
  • Schizophrenic: the charge randomly changes directions at random times.
  • Eccentric Ellipse: the charge moves along a very eccentric ellipse.
  • User Controlled: User can control the charge's path. Use the control pad that pops up.

  • When the charge moves at relativistic speed, the electric field is concentrated near the pole, and consequently the field lines are shifted. The field lines always point to where the charge is at that instant, if we are within the current sphere of information. If that charge has changed speed or direction within a time t < r/c, where r is the distance away, and c is the speed of light, we will not know that charge has accelerated, and the field lines will still point to where the charge would be if it hadn't changed speed or direction.

    Notice That when the charge is accelerated, because the field lines must be continuous, it is forced in a direction almost perpendicular to the the direction of propogation. As time goes on, the line becomes more and more perpendicular, the horizontal component increasing faster than the vertical component. Associated with this electric field is a magnetic field, perpendicular to the electric field and the direction of propogation, which describes light.

    *This applet is only a representation and approximation.

    Physics 1 | Java Applets

    Questions or comments? Send Email to phys1@cco.caltech.edu