# Resistors

## 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 | 10^{6} | 10,000,000 |

k / K | Kilo | 10^{3} | 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.