Electric Current and Resistance in Physics

A current is a river of charge, but the river barely moves. The electrons in a household wire drift along at a fraction of a millimetre per second, and light comes on the instant you flick a switch because the field that pushes them is established almost immediately along the whole wire. Resistance is what makes that drift cost energy, and it depends on the material and the shape of the conductor rather than on the voltage applied. The blocks give the definition of current and the drift model behind it, the resistance relations including how they change with temperature, and the three forms of the power relation that every circuit question eventually needs.