In 1820, a Dane by the name of Hans Christian Ørsted discovered the relationship between electricity and magnetism in a very simple experiment that is shown in the below tutorial. One evening, as Ørsted was setting up materials for a lecture, he brought a compass close to a live electrical wire, and observed that the needle on the compass jumped and pointed to the wire. More experimentation showed that a circular magnetic field surrounded a current-carrying wire. Ørsted had proved that electricity and magnetism were connected and the study of electromagnetism was born.
The equipment in the tutorial models Ørsted's 1820 apparatus. The battery is a voltaic pile constructed of copper and zinc plates in a dilute acid solution. A copper wire is held in place by wooden clamps. Because the battery is not connected, the compass needle points north, attracted solely by the Earth's magnetic field.
Click the Turn On button to connect the battery and create an electric current in the wire, which travels from the positive to the negative terminals. When the current flows through the wire, the compass needle aligns itself with the magnetic field created by the electrons traveling in the current, rather than with the Earth’s magnetic field. Because the magnetic field travels around the wire in a circle (see our Magnetic Field of a Wire tutorial), the compass will point in different directions depending on where it’s placed. If you hit the Flip Battery button to reverse the direction of the current in this tutorial, the magnetic field around the wire will reverse direction, too, as will the compass needle.