# Generator Model

The EJS Generator Model shows a simple electric generator of a loop rotating in a uniform magnetic field. A plot shows the current (in μA) and flux (in arbitrary units). Users can examine and change the model if they have Ejs installed.

## Exercises:

1. Run the simulation with φ = 10*t. Why is this a loop rotating at a constant rate? What is the angular speed of the loop? The arrow on the gray box represents an ammeter, measuring the current in the loop. Record the relation of the loop to the magnetic field when the current is at its maximum/minimum values as well as when the current is zero (in the middle of the ammeter).
2. Observe the ammeter. When it deflects to the right (positive), what direction is the current flowing through the loop (from the blue to the orange or vice versa)? Explain.
3. If the resistance of the loop is 1Ω, its dimensions are 60 cm2, and the current on the plot is measured μAmps, what is the value of the magnetic field (the angle φ is measured in radians and time is measured in seconds)? Notice that on the plot, the current has units of μA but the flux is in arbitrary units (A.U.). Hint: You may find it easier to take data from the plot by opening DataTool (click on the Wrench button) and then clicking the Coordinates check-box. If you want to measure points on the second curve in the window, simply look at the DataTable to the right of the plot and drag the third column in place of the second one (so it is now the active one on the plot).
4. Input a different function for φ(t). Explain what happens and why.

### References:

- Giancoli, Physics for Scientists and Engineers, 4th edition, Chapter 29 (2008).
- Hecht, Physics, 2nd edition, Chapter 20 (2000).

### Credits:

The Generator Model was created by Anne J Cox and Wolfgang Christian 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/>.