A magnetic field forms because of the current flow. This
magnetic field might be considered to expand and move
out from the electromagnet. As the lines of force move
out, the wire will cut them. This wire will therefore have
current induced in it. If the electromagnet is
disconnected from the battery, these lines of force will
disappear and current will stop flowing in the wire.
It can be seen now that current can be induced in a
wire by three methods:
1. The wire can be moved through the stationary
magnetic field (the principle applied in a dc
2. The wire can be held stationary and the
magnet can be moved so the field is carried
past the wire (the principle applied in an ac
3. The wire and electromagnet can both be held
stationary and the current turned on and off to
cause the magnetic field to build up and collapse
so the magnetic field moves one way or the other
across the wire (the principle applied in an
REVIEW 4 QUESTIONS
A magnetic field has what type of lines of force?
When like magnetic poles are brought together,
what action occurs?
What are two parts of a basic electromagnet?