Resistance & Resistors

Resistors are those tiny components within any electronic devices which are so common that we normally ignore them. Let us understand what are these interesting devices and how can they be best used in our circuits.

If you have already studied “Electricity Tutorial”, then you should be familiar with Voltage, Current and Resistance. Else, I suggest you to go back and brush up your knowledge on electricity and resistance before you proceed.

We know that conductors let electricity flow through it, while insulators do not. (Although high voltage might make an insulator to conduct) What we understand from this is Conductors has a low resistance towards the flow of electricity where as insulators have a high resistance. These nifty components called resistors help us by presenting controlled amounts of resistance in any circuits. In other words, Resistors are those devices which control the flow of electricity in a circuit.

Resistors

Resistors are passive devices (do not posses any source of power) made using different materials. The common ones use Carbon or Metal Oxide which is wound around a ceramic core and two copper leads are inserted at both ends of the resistor. The ratio of Carbon/Metal oxide to ceramic core determines the actual resistance of the resistor. When connected in a circuit, these resistors obstruct the flow of electrons resulting in a voltage drop.

Resistor is symbolized as a rectangular box or a zig-zag line in schematic or electrical drawings. However, zig-zag line is an older method and newer drawings prefer the rectangular box. The figure shows two different methods of representing resistor.

Resistor value can be calculated using Ohm’s Law. We know that Ohm’s law states that V=IR, where V is the voltage, I is Current and R is resistance. Hence this equation can be rewritten as R=V/I.
Due to the size limitation, the value of resistor is not printed on it. However, resistor manufactures have a unique color code to specify the value and tolerance, where tolerance is the accuracy of the resistor to the defined value. However, do note that not all color coded components are resistors. They can be capacitors, or inductors which use the same color coding scheme (although they have their numeric values printed on them).

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