Electrical Power and Machines EPE491


Objects which produce their own magnetic field are called magnets.

Magnetic field is the region around a magnet where magnetic effects can be experienced.

A magnetic line of force (or flux line) is a continuous line whose direction at any point is the
direction of the magnetic field at that point.

Fig. 1: Magnetic field

The magnetic flux, Φ through a region is a measure of the number of magnetic field lines
passing through the region.

The ease with which a material will conduct magnetic lines force is called permeability.

An electromagnet is a type of magnet whose magnetic field is produced by the flow of electric
current. The magnetic field disappears when the current ceases.

Magnetic Field

Magnetic fields are the fundamental mechanism by which energy is converted from one form to
another in motors, generators, and transformers.

The magnitude and direction of a magnetic field can be represented by its magnetic flux
density, B.

Four basic principles describe how magnetic fields are used in these devices:
1. A current-carrying wire produces a magnetic field in the area around it.
2. A time-changing magnetic field induces a voltage in a coil of wire if it passes through that
coil. (This is the basis of transformer)
3. A current-carrying wire in the presence of a magnetic field has a force induced on it. (This is
the basis of motor action)
4. A moving wire in the presence of a magnetic field has a voltage induced in it. (This is the
basis of generator action)

D. Johari, FKE UiTM


Electrical Power and Machines EPE491

Production of a Magnetic Field

The basic law governing the production of a magnetic field by a current is Ampere's law.

It is given by:

Hl c  Ni

H – the magnetic field intensity produced by total current Ni
lc – the mean path length of the core...

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