The potential difference between the ends of a wire is given by Vab = IR. Combing that with E = Vab we have E = Vab = IR (ideal source of emf). " That is, when a positive charge flows around the circuit, the potential rise as it passes through the ideal source is numerically equal to the potential drop as it passes through the remainder of the circuit. Once and are known, this relationship determines the current in the circuit."- I cant seem to understand what this means???