Theory

Theory:

Magnetic Force

In 1819, Oersted discovered that a fixed wire carrying an electric current caused a defection of a magnetized compass needle brought near the wire. He found that if a small compass was brought near a wire carrying a steady current the needle was defected so that it tended to point at right angles to the direction of current flow. He also observed that if the compass was placed above the wire the defection was opposite to that when the compass was placed below the wire. Oersted interpreted these effects correctly as an indication that magnetic lines of force are associated with a current flow, and that these lines of force form circles around the current, in the plane perpendicular to the direction of the current flow. The vector quantity magnetic field B was introduced as the source of the magnetic force produced by moving electric charges. The direction of B about a straight wire is shown in Figure 1, with the direction indicated by the arrowheads.

Since the magnetic field produced by a current-carrying wire exerts a force on a second source of magnetic field, such as a compass needle, then there must be an equal but opposite force acting on the current-carrying wire, according to Newton’s Third Law. In other words, when a current-carrying wire is placed in a magnetic field, it experiences a magnetic force exerted by the field.

The physical parameters affecting the magnetic force FB acting on a current-carrying wire are summarized in the following vector equation:

FB=IL*B

That is, the force FB is equal to the current I times the vector (cross) product of the length vector L and the magnetic field B. here the length vector L is defined as a vector that has magnitude L and is directed along the wire segment in the direction of the (controversial) current.

It allows from Equation (1) that the magnitude of the force FB is

FB= ILB sin Ø

Where Ø is the angle between the directions of L and B.

The direction of FB is that of the cross...