This rule is consistent with the field mapped for the long straight wire and is valid for any current segment. (b) Right hand rule 2 states that, if the right hand thumb points in the direction of the current, the fingers curl in the direction of the field. (a) Compasses placed near a long straight current-carrying wire indicate that field lines form circular loops centered on the wire. How does the shape of wires carrying current affect the shape of the magnetic field created? We noted earlier that a current loop created a magnetic field similar to that of a bar magnet, but what about a straight wire or a toroid (doughnut)? How is the direction of a current-created field related to the direction of the current? Answers to these questions are explored in this section, together with a brief discussion of the law governing the fields created by currents.įigure 1. Indeed, when Oersted discovered in 1820 that a current in a wire affected a compass needle, he was not dealing with extremely large currents.
How much current is needed to produce a significant magnetic field, perhaps as strong as the Earth’s field? Surveyors will tell you that overhead electric power lines create magnetic fields that interfere with their compass readings. Use the right hand rule 2 to determine the direction of current or the direction of magnetic field loops. To obtain the magnetic field produced by an electrical current, it is necessary to use the Biot and Savarts law 2:(1) H I 4 d l(r 2 r 1 ) r 2 r 1.Calculate current that produces a magnetic field.
