Ampere's law

Using EMField

Drag a current-carrying wire, with current -5A (hollow green circle) down from the source square at the top of the screen and place it somewhere near the middle of the screen.

    1. Experiment with dragging the mouse to see magnetic field vectors. Click to deposit a vector on the screen.
      If you want to clean up the screen, click on the Clear button.
    2. Deposit field vectors in a radial pattern around the current, at several distances from the wire. Is conventional current flowing into or out of the screen? (Use your right hand).
    3. Move the wire. What happens?
    4. Drag the existing wire back onto its source box to delete it, and replace it with a wire carrying a current of +5A.
    5. Again deposit field vectors in a radial pattern around the current. Is this current into or out of the screen?

Ampere's Law

    1. Leave the +5A current on the screen.
    2. From the Measure Type pull-down menu, choose Ampere's Law
    3. Place the mouse near the current. Drag the mouse in a counterclockwise direction completely around the current. The line shows
    4. Is the result positive or negative?
    5. Repeat this, making a circle of much larger radius around the current. Why is the result for the same ?
    6. Drag the mouse clockwise around the current. What is different?
    7. By convention, we take a counterclockwise path, and interpret a positive result as corresponding to conventional current out of the page.

The effect of currents not inside the path

    1. Clean up the screen, leaving a +5A current on the screen.
    2. Drag the mouse in a circular path near but not enclosing the charge.
    3. Explain why comes out to be zero.
    4. Experiment with several currents, and try paths that enclose some, all, or none of them.