Abstract
Electric current—the flow of electric charge—is indispensable to modern society. When Ohm's law applies, resistance (R) depends on the geometry of the object and the type of material but not on the current or electromotive force (emf). For wires, where the electrodes are attached at the ends, R is proportional to the length and inversely proportional to the cross-sectional area. Thus, overall, R is inversely proportional to the linear dimension. When an overall voltage difference △V is applied between two terminals connected to an ohmic material, leading to a total current I through the material, Ohm's law in its overall, or global, form applies. This chapter provides the local form of the Ohm's law . If the connections to an object change, the resistance will change. When resistors are connected in series, the voltage across the equivalent resistance is the sum of the voltages across each resistor and when in parallel, the current through the equivalent resistance is the sum of the currents through each resistor. emf is measured by potentiometers. The chapter discusses voltaic cells in detail.
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