Pendulum created by two current carrying wires.

# Current Wire Pendulum Model

The EJS Current Wire Pendulum models the force between two current carrying wires suspended from a support to create two linked pendula. The current in each wire and the angle between each pendulum and the vertical can be changed and the motion can be damped. Users can examine and edit the model if Ejs is installed. Information about EJS is available at: <http://www.um.es/fem/Ejs/>.

## Questions:

1. Run the simulation. You can click-drag in the the window to rotate the view and shift-click to zoom in and out. The color-coded sliders control the current (in Amps) in each long wire. When the simulation is paused, you can change the initial angle for each wire (angle is measured from the vertical). The v=0 button damps the motion. Does the current flow in the same direction in both wires? Explain.
2. Reset the simulation. What is the equilibrium position of the wires when the current is 200 A in each?
3. If the current is not the same in each wire, what does the equilibrium position look like? It is possible to determine (without the color coding), which current you are adjusting? Why or why not?
4. The line connecting each wire to the central support is 1 m. What is the mass/length of each wire (it is the same for both).
5. What would be different if the mass/length were different for each wire?
6. Optional: If you have EJS installated, change the simulation so that each wire has a different mass/length (Note: Uses an array).

### References:

- Halliday, Resnick and Walker, Fundamentals of Physics, 8th edition, Chapter 29 (2007).

### Credits:

The Current Wire Pendulum Model was created by Anne J Cox using the Easy Java Simulations (EJS) authoring and modeling tool.

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/>.