## Overview

Resistors are possibly one of the most common components that you will use. A resistor has three properties that should be considered when working with an electrical circuit:

• Resistance
• Tolerance
• Power rating

For a more in-depth discussion about resistors and resistance, check out Part 4 of the Electronics Tutorial.

### Resistance

Resistance is measured in Ohms symbol (`Ω`). This may also be prefixed with a letter to indicate the scale of the value. Common scale factors relevant to resistors are:

Letter Prefix Magnitude Value
M Mega 106 10,000,000
k / K Kilo 103 10,000
m milli 10-3 0.001

Therefore, a `1kΩ`; resistor has a resistance of `1,000Ω`;.

The prefix letter may also be used to indicate the location of a decimal point. For example, a `4K7` resistor has a resistance of `4.7kΩ`.

### Tolerance

The tolerance is expressed as a percentage. Common tolerances are 1%, 5% and 10%. Lower tolerance resistors are more expensive due to the higher requirements of the manufacturing process.

A `4.7kΩ` resistor with a 5% tolerance could have a value between 4,`465Ω` and `4,935Ω`.

### Power Rating

Resistance to the passage of electrical current generates heat. The amount of heat generated can be calculated using the following formula:

``````P = I x V
``````

The power is stated in Watts (`W`) and the power rating of the resistor should always be greater than the product of the current (`I`) flowing through the resistor and the voltage (`V`) drop across the resistor.

## Schematic Symbol

There are two possible symbols used in circuit diagrams (schematics):

• Zig-zag line (IEEE)
• Rectangle (IEC)

The use zig-zag line is more commonly used in America than the rectangle.