a. Current flowing through a conductor always produces a magnetic field around
that conductor. Under certain conditions, a magnetic field can also produce current flow
in a conductor. Technically, however, it is more acceptable to say that a magnetic field
can produce an EMF and that this EMF (voltage) can cause current flow when there is a
complete circuit. Whenever a conductor forming part of a closed circuit cuts across
magnetic lines of force, an electric current is induced in the conductor. In 1831,
Faraday demonstrated this principle by rapidly moving a wire through a magnetic field,
causing an electric current to flow in the wire.
b. The magnitude of the induced voltage is dependent upon four factors:
(1) The speed or rate at which the wire moves. The more quickly the wire
moves, the more lines of force it will cut.
(2) The strength of the magnetic field. When the lines of force are closely
concentrated, the conductor cuts more lines per second.
(3) The angle between the motion of the conductor and the direction of the
magnetic lines of force. As the angle approaches 90, the voltage increases in
magnitude because more lines of force are being cut per second (figure 2-11).
Figure 2-11. Various angles between the moving conductor and the lines
of magnetic force.