reading this section you will be able to do
how current can be induced in a conductor without making contact.
the process of induction.
We have now seen that if electrical
current is flowing in a conductor, there is an associated magnetic
field created around the wire. In a similar manner, if we move
a wire inside a magnetic field there will be an electrical current
that will be generated in the wire.
Current is produced in a conductor
when it is moved through a magnetic field because the magnetic
lines of force are applying a force on the free electrons in the
conductor and causing them to move. This process of generating
current in a conductor by placing the conductor in a changing
magnetic field is called induction. This is called induction
because there is no physical connection between the conductor
and the magnet. The current is said to be induced in the conductor
by the magnetic field.
One requirement for this electromagnetic
induction to take place is that the conductor, which is often
a piece of wire, must be perpendicular to the magnetic lines of
force in order to produce the maximum force on the free electrons.
The direction that the induced current flows is determined by
the direction of the lines of force and by the direction the wire
is moving in the field. In the animation above the ammeter (the instrument used to measure current) indicates when there is current in the conductor.
If an AC current is fed through a
piece of wire, the electromagnetic field that is produced is constantly
growing and shrinking due to the constantly changing current in
the wire. This growing and shrinking magnetic field can induce
electrical current in another wire that is held close to the first
wire. The current in the second wire will also be AC and in fact
will look very similar to the current flowing in the first wire.
It is common to wrap the wire into
a coil to concentrate the strength of the magnetic field at the
ends of the coil. Wrapping the coil around an iron bar will further
concentrate the magnetic field in the iron bar. The magnetic field
will be strongest inside the bar and at its ends (poles).