I'm a computer science student. I'm currently learning electronics so that I can program embedded devices effectively. I'm reading from the free book at allaboutcircuits.com. Why is the voltage between two points on a wire in a closed circuit equal to zero? Note that between these two points there is no resistance; Think about it as a wire with no other electric devices attached in between these two points. Here is an illustration of what I mean: (taken from allaboutcircuits.com) My question is, why is the voltage between 1 and 2 (or, 3 and 4) zero, but that of 2 and 3 not? I can't understand how these two have different voltages. Here is what I understand: The current in the whole circuit is affected by the resistance of the lamp, because the potential energy of the battery is trying to "push" electrons with a certain amount of force per unit charge, but the resistance of the lamp will make this push "slower". Think about electrons in the circuit as marbles arrayed along the wire. At any point, if there is a resistance, the whole "push" of electrons (i.e. marbles) in the whole circuit will be "slowed". That results in a lower current (i.e. the whole array of marbles which spans the wire will be slowed in movement). Voltage is the measure of electric potential energy per unit charge (Columb). It is a result of imbalance of electrons (one matter has an excess of electrons from another matter which now has a deficiency of electrons-that's why it measured between two points). This imbalance creates that electric potential energy, which is "actualized" in the form of a force pushing electrons back to their original matter to balance the excess/deficiency.