The principles ofmagnetism are an integral part of electricity.
In fact, magnetism can be used to produce electric current and
When we think of a permanent magnet, we often envision a
horse-shoe or bar magnet or a compass needle, but permanent
magnets come in many shapes. However, all magnets have two
characteristics. They attract iron and, if free to move (like the
compass needle), a magnet assumes a north-south orientation.
Magnetic Lines of FluxEvery magnet has two poles, one north pole and one south
pole. Invisiblemagnetic lines of flux leave the north pole and
enter the south pole. While the lines of flux are invisible, the
effects of magnetic fields can be made visible. When a sheet
of paper is placed on a magnet and iron filings loosely scattered
over it, the filings arrange themselves along the invisible lines of
The density of these lines of flux is greatest inside the magnet
and where the lines of flux enter and leave the magnet.
The greater the density of the lines of flux, the stronger the
Interaction BetweenWhen two magnets are brought together, the magnetic flux
Magnetsaround the magnets causes some form of interaction. When
two unlike poles are brought together the magnets attract each
other. When two like poles brought together the magnets repel
ElectromagnetismAn electromagnetic field is a magnetic field generated by
current flow in a conductor. Every electric current generates a
magnetic field and a relationship exists between the direction
of current flow and the direction of the magnetic field.
Theleft-hand rule for conductors demonstrates this
relationship. If a current-carrying conductor is grasped with the
left hand with the thumb pointing in the direction of electron
flow, the fingers point in the direction of the magnetic lines of
Current-Carrying CoilA coil of wire carrying a current, acts like a magnet. Individual
loops of wire act as small magnets. The individual fields add
together to form one magnet. The strength of the field can
be increased by adding more turns to the coil, increasing the
amount of current, or winding the coil around a material such as
iron that conducts magnetic flux more easily than air.
Theleft-hand rule for coils states that, if the fingers of the left
hand are wrapped around the coil in the direction of electron
flow, the thumb points to the north pole of the electromagnet.
An electromagnet is usually wound around a core of soft iron
or some other material that easily conducts magnetic lines of
A large variety of electrical devices such as motors,
circuit breakers, contactors, relays and motor starters use
1. The two characteristics of all magnets are: they attract
and hold ________, and, if free to move, they assume
roughly a ________ position.
2. Lines of flux always leave the ________ pole and enter
the _________ pole.
3. The left-hand rule for conductors states that, when the
left hand is placed around a current-carrying conductor
with the thumb pointing in the direction of ________
flow, the fingers point in the direction of ________.