Electronics >> Resistors

Resistors are one of the basic electronic components and are designed to have a certain amount of resistance to the flow of electricity. [Resistor schematic symbols] [Ohm's Law]

The main applications of Resistors are:

• Limit current
• Divide voltage

Resistors come in many different shapes, sizes and values however they are generally placed under two main categories:

• Fixed value
• Variable (e.g. Photoresistor, Potentiometer, Rheostat)

(Potentiometers are used in circuits to divide voltage whereas rheostats are used to control the flow of current.)

Unit to measure and indicate resistance is called Ohm, and is presented by the Greek symbol Omega Ω.   (e.g. 1kΩ, 220Ω)

The value of most fixed Resistors are indicated by color code.

Four-Band color coded Resistors.

Tolerances of ±5%, ±10%, (±20% when no tolerance band)

Five-Band color coded Precision Resistors.

Tolerances of ±1%, ±2%

Depending on the type, the value of some Resistors like Surface-mount resistors are indicated by alphanumeric value. The tolerance of these resistors could also be displayed using an alphabetical value indicator.

(F ±1%, G ±2%, J ±5%)

Some examples:

• 590F » 590 Ω ±1%
• 4R7G » 4.7 Ω ±2%
• 56KJ » 56k Ω ±5%

When selecting or identifying a Resistor we also need to keep in mind the value of the Wattage that the Resistor is rated for. This value is directly related to the capability of the component to dissipate heat.

(e.g. ¼ Watt, ½ Watt, etc...)

 

The formula used to calculate the resistance is called Ohm's law, and it explains the relationship between voltage, current and resistance in a circuit.

As it is demonstrated Ohm's law is also used to calculate voltage and current of a circuit.

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