Resistor

It is a device or electronics components, which opposes flow of current.

Function- Resistors restrict flow of electric current, i.g. a resistor is placed in series with a Light-Emitting Diode (LED) to limit the current passing through it.

Resistance is measured in ohms. Symbol for ohm is an omega ohm.
1 ohm is quite small so resistor values are often given in k ohm and M ohm.
1 k ohm =1000 ohm
1 M ohm =1000000 ohm.
Resistor values are normally shown using colored bands.
Most resistors have 4 bands:



First band gives first digit, second band gives second digit while third band indicates number of zeros. Fourth band is used to shows tolerance (precision) of resistor, this may be ignored for almost all circuits but further details are follow-
This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.
So its value is 270000 ohm = 270 k ohm.
On circuit diagrams the ohm is usually omitted and the value is written 270K.

Types of Resistor-
1. Low Power Resistor- Low power resistance is used in low current area. These are available in ¼w, ½w,1w, 2w
2. High Power Resistor- High power resistance is used in high current area. These are available in more than 5w to 100w. High power resistor are of two types-
a). Fixed Resistors: It is one in which the value of resistance can’t change. These resistor used in monitor, UPS, SMPS etc.
b). Tapped Resistor: These resistors are used in regulators, stabilizers and washing machines etc.

3. Variable Resistor- There are two general ways in which variable resistors are used. One is variable resistor which value is easily changed, like volume adjustment of Radio. Other is semi-fixed resistor that is not meant to be adjusted by anyone but a technician



This symbol is used to indicate a variable resistor in a circuit diagram.

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