In an electric field, especially in a conductor, charged particles will move according to the electromotive force applied by the electric field. In a practical sense, the charged particles in question are the free electrons in the conductor. Electrons are attracted to the areas of positive charge, and are repelled from the area of negative charge.
The mass-flow of electrons through a conductor is known as electric current.
Units of Current
The flow of electrons through a conductor is measured in Amperes. The electric potential that causes electrons to flow is measured in Volts.
Since ancient times, people have known about special rocks and materials that display a certain attractive and repulsive force on other such rocks. Termed "magnets", the force between them operates on a similar principle to the electric force that we have studied so far.
All magnets have two sides or poles, dubbed "North" and "South". Like positive and negative charges, like poles repel and opposite poles attract. The magnetic force works over distance, with the effect of the magnet decreasing over distance.
Electric currents, or moving electric fields produce a magnetic force.
Like an electric field, there is a magnetic field that extends everywhere. the strength of the magnetic field is dependent on the location of magnets in the field. It is a vector field, so every point has both a strength and a direction.
We will discuss the mathematical determination of the magnetic field starting in the next chapter when we discussion the Biot-Savart Law.
Field of a Current
the magnetic lines of forces are wrongly shown in the figure as the current is traveling downwards the magnetic lines of force will pop out of the page from the left of the wire and go into the page on the right side