PURPOSE: To show that a magnetic field is created by a current wire.
DESCRIPTION: A stiff wire is clamped to stand upright on the overhead as shown in the photo at left. A low voltage DC power supply provides a 10 amp current to the wire. A compass needle probed around the wire will show the direction of the magnetic field around the wire due to the current, as shown in the middle photo. The magnetic field can also be visualized by sprinkling iron filings around the wire.
The Oerstead aparatus, shown in the photo at right, can also be used.
EQUIPMENT: The large wire loop is stored in the electricity and magnetism cabinet.
SETUP TIME: Place the compass needle to point at the wire when the current is off and only the earth's field is present. This way when the power switched is turned on the needle will deflect to point perpendicular to the wire. Also, keep the power supply at some distance from the needle or the transformer may influence the magnetic field. Also, some overheads contain permanently magnetized transformer laminations that will influence the direction of the compass needle.
Updated by Jun Qi in 3/13/2000