c. A magnetic field exists about a wire only durinq the time the current is flowing.
When the current ceases to flow, the magnetic field around the wire collapses.
d. The strength or intensity of the magnetic field around a current-carrying
conductor increases or decreases when the current increases or decreases. Reversing
the direction of current in the conductor reverses the direction of the magnetic field.
2-16. PRODUCTION AND USE OF ELECTROMAGNETIC FORCE
a. If a conductor through which a current is flowing is bent in the form of a loop,
the same circular lines of force (magnetic field) surrounds the conductor as when it is
straight. Therefore, all the lines of force enter on one side (face) of the loop and leave
on the other side, resulting in a north pole on one face and a south pole on the other. If
several loops or turns of wire are so wound as to form a coil, it is called a helix or a
solenoid (figure 2-10A). During current flow, the intensity of the magnetic lines of force
around such a coil of wire are proportionately greater than those around a single loop of
b. If a piece of magnetic material--usually soft iron--is placed within a solenoid
through which current is flowing, the magnetic properties of the solenoid are
tremendously increased. The inside of any coil is termed the core and, if the coil is
wound on a core of magnetic material, it acts as an electromagnet (figure 2-10B).
c. Electromagnets are widely used in electrical equipment, for example, the
and electrical measuring instruments. The principle of the electromagnet is utilized in
many of the devices in an x-ray circuit such as relays, remote control switches, and
Figure 2-10. Relationship between solenoid and electromagnet (description in text).