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In a vacuum, the curl of this quantity is "1 over c-squared, partial-E partial-t." A differential bit of it is proportional to "I, d-l cross r, all over r cubed." A constant that determines it has numerical value "4-pi times 10 to the negative 7." The line integral of this quantity equals "mu-nought times I-enclosed." Its divergence, or its integral around a closed surface, is (*) zero, by Gauss's law, which states the impossibility of this kind of monopole. One of these things exerts a force proportional to the sine of the angle between it and a current-carrying wire. One of these generated by a current is modelled by the Biot-Savart ["BEE-oh sa-VAR"] and Ampère's laws. For 10 points, name this counterpart to the electric field.
In a vacuum, the curl of this quantity is "1 over c-squared, partial-E partial-t."
magnetic field [or B-field; accept H-field; prompt on any answer just about "magnets" in general]