Remember that electrons have a negative electrostatic field surrounding them. When energy from a power source such as a battery is applied to a circuit, making the electrons flow through a conductor, a new type of field is developed around the wire. This is called an electromagnetic field. You can learn more about why this field develops in the materials about magnetism.
As we can see in the diagram below, the magnetic field that surrounds a current-carrying conductor is made up of concentric lines of force. The strength of these circular lines of force gets progressively smaller the further away from the conductor we get. Also, if a stronger current is made to flow through the conductor, the magnetic lines of force become stronger. As a matter of fact, we can say that the strength of the magnetic field is directly proportional to the current that flows through the conductor.
The term field intensity is used to describe the strength of the magnetic field. From now on we will use this new term to describe this field that is developed around a conductor that is carrying electrical current.
We have determined that this magnetic force field is a result of current flowing in a conductor. We have also shown that the field is circular in shape. What we do not yet know is what direction the circular field is in.
Field Direction (The Right-hand Rule)
A number of different rules have been developed to help determine the direction of the magnetic field relative to the current. “The right-hand rule”
is the simplest to remember and can be used to determine the direction
of the electromagnetic field around a current carrying conductor. With
this rule when the thumb of the right-hand is pointing in the direction
of current flow, the fingers will be pointing in the direction of the
magnetic field.
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