... 4a. Electric Fluid . ... Field Lines . ... EM Waves . ... One could then define the unit of current, as the current which, when flowing in a straight wire, attracts a similar current in a parallel wire 1 meter away with a force of unit strength, for every meter of the wires' length. ... Faraday also showed that a magnetic field which varied in time--like the one produced by an alternating current (AC)--could drive electric currents, if (say) copper wires were placed in it in the appropriate way. ...

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Educator's Guide to Impact Craters . ... Just about all craters have deep central depressions, raised rims, and a blanket of ejected material surrounding them. ... Look for classical cratering features: basin, raised rim, ejecta blanket (material excavated from the crater and dumped around it, visible as white flour on the colored powder), and rays (material shot out at high velocity forming lines pointing directly away from the impact site). ... The material lies like a blanket around the crater. ...