Demos: 6D-04 Earth Magnetic Field Inductor
A 30-cm diameter coil of wire having a large number of turns is connected to a projectable microammeter. The coil, held in the hand is tipped rapidly back and forth so that it is oriented alternately parallel and perpendicular to the earths magnetic field. The ammeter shows that an emf is induced alternately in opposite directions as the plane of the coil cuts through the field lines.
Directions: Hold the coil in front of you with its plane in the vertical direction. Rapidly wiggle the coil back and forth (about an axis along your arm). The faster the wiggle, the greater the induced emf.
Suggestions for Presentation: After discussing magnetic induction, you can simply pick up the coil and wiggle it back and forth, showing the induced emf. Ask the students how a magnetic flux can be changing at the coil when there is no apparent source of a B-field. This can then lead to the fact that there is present in the room the magnetic field of the earth. The field is relatively weak. Discuss the make-up of the coil with regard to its sensitivity (large area, large A; many turns, large N; and a fast movement, small t ).