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The magnetic field (marked B, indicated by red field lines) around wire carrying an electric current (marked I) Compass and wire apparatus showing Ørsted's experiment (video [1]) In electromagnetism, Ørsted's law, also spelled Oersted's law, is the physical law stating that an electric current induces a magnetic field. [2]
The magnetic field of permanent magnets can be quite complicated, especially near the magnet. The magnetic field of a small [note 6] straight magnet is proportional to the magnet's strength (called its magnetic dipole moment m). The equations are non-trivial and depend on the distance from the magnet and the orientation of the magnet.
Two current-carrying wires attract each other magnetically: The bottom wire has current I 1, which creates magnetic field B 1. The top wire carries a current I 2 through the magnetic field B 1, so (by the Lorentz force) the wire experiences a force F 12. (Not shown is the simultaneous process where the top wire makes a magnetic field which ...
[6] [7] He investigated and discovered the rules which govern the field around a straight current-carrying wire: [8] The magnetic field lines encircle the current-carrying wire. The magnetic field lines lie in a plane perpendicular to the wire. If the direction of the current is reversed, the direction of the magnetic field reverses.
When electricity flows (with direction given by conventional current) in a long straight wire, it creates a cylindrical magnetic field around the wire according to the right-hand rule. The conventional direction of a magnetic line is given by a compass needle. Electromagnet: The magnetic field around a wire is relatively weak. If the wire is ...
This is similar to the magnetic field produced on a plane by an infinitely long straight thin wire normal to the plane. This is a limiting case of the formula for vortex segments of finite length (similar to a finite wire): v = Γ 4 π r [ cos A − cos B ] {\displaystyle v={\frac {\Gamma }{4\pi r}}\left[\cos A-\cos B\right]} where A ...
By combining the Lorentz force law above with the definition of electric current, the following equation results, in the case of a straight stationary wire in a homogeneous field: [30] =, where ℓ is a vector whose magnitude is the length of the wire, and whose direction is along the wire, aligned with the direction of the conventional current I.
The magnetic vector potential, , is a vector field, and the electric potential, , is a scalar field such that: [5] = , =, where is the magnetic field and is the electric field. In magnetostatics where there is no time-varying current or charge distribution , only the first equation is needed.