Resistance

Electrical Circuit Analysis

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What is Electrical Resistance?

Electrical resistance of an object is a measure of its opposition to the flow of electric current.
Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance.

Fig. 1: Electrical resistance.

The resistance in a wire increases as:

The length of the wire increases
The thickness of the wire decreases.

An electric current flows when electrons move through a conductor, such as a metal wire. The moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow, and causes resistance.

The resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through. The relationship between resistance and wire length is proportional.

Fig. 2: Cross-sections of thin and thick wires

The higher the resistance, the lower the current flow. If abnormally high, one possible cause (among many) could be damaged conductors due to burning or corrosion. All conductors give off some degree of heat, so overheating is an issue often associated with resistance.

The lower the resistance, the higher the current flow. Possible causes: insulators damaged by moisture or overheating. Many components, such as heating elements and resistors, have a fixed-resistance value. These values are often printed on the components' nameplates or in manuals for reference.

"Resistance" may sound negative, but in electricity it can be used beneficially.

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