Final answer:
To identify their value many resistors are marked with four colored bands.
Step-by-step explanation:
Resistors are marked with colored bands to identify their value, resistance, tolerance, and multiplier.
The first two colored bands represent the first two digits of the resistance value of the resistor, while the third band is a multiplier that is used to calculate the actual resistance value.
The fourth band represents the tolerance of the resistor, which is its precision or accuracy of the resistance value. For instance, a resistor has a resistance of 20 × 10^5 ± 10% according to the color bands.
This means the resistor has a resistance of 2 million ohms with a tolerance of ± 10%. Knowing how to read these color bands is essential when working with electronic circuits, as it allows one to understand the attributes of the resistor without electronic testing tools.