Current Loops



A cross section of a circular wire loop carrying an unknown current is shown.   The arrows represent the direction of the magnetic field.  The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black.  You can double-click in the animation to add magnetic field lines, click-drag the center of the loop to reposition it, and click-drag the top or bottom of the loop to change its size.  You may also add a compass by clicking the “Add Compass” link.


Does current flow out of the red (top) end or the blue (bottom) end?  


Instructor Resources

Reference: See Giancoli-PA: 20-2, Giancoli-SE: 27-2.
Answer: The current comes out of the red (the top) end and into the blue (the bottom) end. Use the right- hand rule on either cross section and compare the curl of your fingers with the magnetic field vectors. Again, the use of the compass can be used in conjunction with the magnetic field vectors. Another interesting thing to do here is to drag the end of the wire to shrink the loop down to a zero radius. What should the compass needle do? Try it.
Script Author: Mario Belloni