Magnetic Field Generated by Current
(a) Compasses placed near a long straight current-carrying wire indicate that field lines form circular loops centered on the wire. (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. This rule is consistent with the field mapped for the long straight wire and is valid for any current segment.
Source
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"OpenStax College, Magnetic Fields Produced by Currents: Ampere’s Law. November 19, 2012."
http://cnx.org/content/m42382/latest/#import-auto-id1166991852141
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