Magnetic Field About a Conductor Carrying Current

Author: E.E. Kimberly

An electric current flowing in a conductor produces a magnetic field around that conductor. Fig. 1-5 shows the direction of this field when the current flow is toward the observer. A dot (suggesting the point of an arrow) on the cross-section of a conductor conventionally represents current or emf toward the observer. A cross or plus sign (suggesting tail feathers of an arrow) represents current or emf away from the observer. If the conductor be grasped by the right hand with the thumb pointing in the direction of current flow, then the fingers will point in the direction of the magnetic lines of flux around the conductor, as shown in Fig. 1-5. This is the magnetic rule of thumb.

Fig 1-5 Use of Rule of Thumb