Electrostatic Field

After reading this section you will be able to do the following:

  • Compare the definitions of a magnetic field (from the previous page) and an electrostatic field.
  • Describe what field intensity is and how it is determined.
  • Explain the "right-hand rule."

Electrostatic Field

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 Magnetism module.

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.

When electrons flow, a magnetic field that is perpendicular to the current flow is induced. For the case of current in a wire, the magnetic field circles around the wire getting weaker with distance away from the wire.

Field Intensity

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)

When current flows through a wire you can point your right thumb parallel to the length of the wire. The direction of your curled fingers

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.

Review

  1. Field intensity is a term used to describe the strength of the electromagnetic field.
  2. Field intensity is determined by the amount of electrical current flowing in the wire.
  3. The right-hand rule can be used to describe the direction of the electromagnetic field.