Electricity and Magnetism : AC - DC Generators / A Series/Parallel Circuit Puzzle / Circle of Magnetism / Dynamo 1/ Dynamo 2 / Induced Current - Eddy Currents / Lenz's Law / The Magnetic Field - Lines of Force / The Rotating Copper Disk / Pepsi Can / Helmholtz Coils / Electrons Beam
Circle of Magnetism

How all the compass needles point in the same direction. The magnetic field of the  earth is in the  North-South direction this is by the magnetized compass needles.

When we rotate the table top and see  how the compass needles continue pointing North.

However, when we press the button on the leg of the stand. The needles near the center of the table top are all pointing in a circle as if they were playing a children’s game

WHY?        

 A strong electrical current is flowing through the vertical shiny wire. The current generates a circular magnetic field much stronger than the earth’s field.

 Now, we rotate the table top again. The needles near the center of the table top are all still pointing in a circle as before. The needles far from the center of the table e are not still pointing in a circle as before. But neither are they pointing north as at the beginning. The compass needles seem somewhat confused.

WHY?        

The strength of the magnetic field is weakest  at a large distance from the wire.  Here the magnetic field of the earth and the one generated by the wire are add to.