Preparation: Force/Electromagnetic/ExB/Explain It.

The force experienced by a charged particle moving in an electric or in a magnetic field are quite different. The simulation on Page 2 lets you explore the motions of a charged particle in a pure electric field or a pure magnetic field, or in a combination of the two when the two kinds of fields are at right angles to each other.

An electric field is present that is uniform throughout the applet window. It is indicated by the red arrow in the top left corner. You can change it or set it to zero by dragging the arrow at its tip.

A magnetic field is present that is uniform throughout the applet window. It is perpendicular to the screen, either into the screen or out of the screen. You can change this direction by clicking the B-toggle button. You can change the magnitude of the magnetic field or set it to zero by means of the B-slider.

The initial velocity of the charged particle is represented by the green arrow. You can vary it dragging the tip of the arrow .

You can use the scale to make relative measurements of the particle's initial speed. The scale can be dragged, by clicking somewhere at its middle, and its orientation can be changed by dragging either end point of the scale.

You can also vary the following:

• the number of particles, choosing between 1, 2, or 12, by means of a slider
• the sign of the charge and the magnitude of the charge-to-mass ratio of the particle(s) (all particles are identical)

Finally, you can either display or not display the particle track(s), by means of a toggle button, and either let the simulation run uninterrupted or step through the motion, by clicking either the PLAY or STEP buttons.