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:
- Power rating
For a more in-depth discussion about resistors and resistance, check out Part 4 of the Electronics Tutorial.
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:
|k / K||Kilo||103||10,000|
1kΩ; resistor has a resistance of
The prefix letter may also be used to indicate the location of a decimal point. For example, a
4K7 resistor has a resistance of
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.
4.7kΩ resistor with a 5% tolerance could have a value between 4,
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.
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.