Charge Motion In A Potential Valley Applet

Instructions

This applet is designed to allow you to explore charged particle motion in an electrostatic potential "valley". It also illustrates graphically that the electric field "pulls" parallel to itself by showing the field lines as a particle tries to leave a region of field which is attractive.

WARNING: For some versions of Netscape, the RESTART botton works fine as long as you never go away from the canvas with the charges on it. However it you page down and come back, it no longer works. The applet seems to freeze, and to get it to work again you have to quit the browser and restart. Hitting RELOAD does not help. This is not a problem on other versions of Netscape or on Explorer.

In particular, we have one free particle with charge -q which is attracted to two particles both with charge +Q. The +Q charges are fixed in position on the y-axis at +150 meters and -150 meters respectively. The particle that is free to move is initially at the origin moving in the positive x-direction with speed v. We integrate the equation of motion of the free charge using

where for this situation Q = 10 q and

The potential that the charge moves in looks (as seen along the x-axis) like this:

The motion of the particle conserves the value of

To start the integration, click on the "Go" button. After the integration is finished, change the parameters as you desire, hit "Restart", and click on the "Go" button to run the integration again with different parameters.

To get this applet to run faster on a slow computer, increase "Faster" by upping that parameter with the scroll bar on the upper left. To get "smoother" field lines, reduce this parameter.

To increase the initial particle velocity in the x-direction, use the scroll bar second from the left. Clicking on the arrows of the scroll bar will change the value of v by 1 meter/sec; clicking inside the field but not on the bar itself with change the value of v by 10 meters/sec. You can also change the value of v by clicking on the bar itself and dragging it.