Chapter 30187Q30.12Maxwell included a term in Ampère’s law to account for the contributions to the magnetic field bychanging electric fields, by treating those changing electric fields as “displacement currents.”Q30.13Mmeasures the intrinsic magnetic field in the nail. Unless the nail was previously magnetized, thenMstarts out from zero. His due to the current in the coil of wire around the nail. Bis related to thesum of Mand H. If the nail is aluminum or copper, Hmakes the dominant contribution to B, but Mcan add a little in the same or in the opposite direction. If the nail is iron, as it becomes magnetizedMcan become the dominant contributor to B.Q30.14Magnetic domain alignment creates a stronger external magnetic field. The field of one piece of ironin turn can align domains in another iron sample. A nonuniform magnetic field exerts a net force ofattraction on magnetic dipoles aligned with the field.
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