Resistors A resistor is an electrical circuit element made out of a material that conducts electrical current, but not as well as a metal wire. Electrical current (I) is the flow of electrical charges, and in direct current(DC) circuits, is pictured as going the opposite direction to that of the flow of electrons from the negative side of the voltage source to the positive side. Current, then, flows from plus to minus and relates to charge through the equation I=dQ/dt. Every electrical device in existence, from light bulbs to cell phones, naturally exhibits resistance, but circuit components called resistors are also manufactured that serve no other purpose than to structure the balance and flow of voltage and current in a circuit. These devices are usually quite small and varied, but an idealized version is depicted to the right. It has a cross-sectional area Aand an overall length d. The material from which it is constructed has an inherent electrical parameter called the resistivity, ρ, and so the
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