Resistors are classified primarily by which two characteristics?

Resistors are fundamentally defined by their electrical properties, which include Ohmic resistance and power rating. Ohmic resistance is measured in ohms and indicates how much the resistor opposes the flow of electric current. This characteristic is crucial for determining how much current will pass through the resistor at a given voltage, following Ohm's Law.

The power rating, typically expressed in watts, specifies the maximum amount of power the resistor can safely dissipate without being damaged or failing. Understanding both the resistance and the power rating is essential for proper application to ensure that the resistor operates safely within its limits in an electrical circuit.

While size, shape, and color may sometimes provide useful information about a resistor, particularly in visual identification or classification, they do not define the electrical function or capabilities of the resistor. Therefore, they are secondary to the primary factors of Ohmic resistance and power rating when it comes to effectively selecting and integrating resistors in electronic designs.