Screen shot of the
dipole and test charge.
Dipole Trajectory Model
The EJS Dipole Trajectory
model shows the electric field generated by a dipole. A slider can
change
the separation between the charges. A test charge, with an adjustable
initial position, is released from rest in the electric field.
Users
can examine the model if
Ejs is
installed.
Exercises:
- Run
the simulation and observe the dipole field due to fixed charges (red
and blue) . Also note the trajectory of the test charge.* You can move
the test charge anywhere on the screen (except on top of one of the
stationary charges). You can also change the separation between the two
fixed charges.
- Many students are surprised to find that the test charge does not
follow the field or go along the direction of the arrows. Explain the
motion of the test charge (specifically why it doesn't follow the field
arrows)? Where can you place the charge initially so that it does
follow the field arrows? Explain.
*Recall that a test charge
is defined to feel the effects of an external electric field, but not
change the field itself (therefore, there are no field vectors around
it).
References:
- Giancoli, Physics
for Scientists and Engineers,
4th
edition, Chapter
21
(2008).
Credits:
The Dipole Trajectory
Model
was
created by Anne J Cox, Wolfgang Christian, and Francisco
Esquembre using the Easy Java Simulations (EJS) authoring and
modeling
tool. Exercises written by Anne J Cox.
You can examine and modify a
compiled EJS model if you run the
program by double clicking on the model's jar file.
Right-click
within the running program and select "Open EJS Model" from the pop-up
menu to copy the model's XML description into EJS. You must,
of
course, have EJS installed on your computer.
Information about EJS is
available at: <http://www.um.es/fem/Ejs/>
and in the OSP ComPADRE collection <http://www.compadre.org/OSP/>.
