Resistance is a property of all electrical components. Sometimes the effect of resistance is undesirable; other times it is constructive. Resistors are components manufactured to possess a specific value of resistance to the flow of current. A resistor is the most commonly used component in an electronic circuit.

Resistors are available with fixed or variable resistance values. They are available in a variety of shapes and sizes to meet specific circuit, space, and operating requirements .

Resistors are drawn schematically as a series of jagged lines. A resistor’s tolerance is the amount that the resistor may vary and still be acceptable. It is expensive for a manufacturer to hold a resistor to a certain value when an exact value is not needed.

Therefore, the larger the tolerance, the cheaper it is to manufacture. In most electronic circuits, resistors of 10% tolerance are satisfactory.

tors fall into three major categories, named for the material they are made of :

• molded carbon composition resistors
• wirewound resistors,
• carbon film resistors.