CompTIA A+® Certification All-In-One For Dummies®, 2nd Edition

6.1. Knowing the Basics of Power Terminology

You should learn four terms that deal with power in computer systems: volts, amps, ohms, and watts. If you have a firm grasp on how they relate to each other, you can understand how power is measured and used within computer systems. Electrical current flows with the same principles that are used when water flows, so water is often used as an analogy for electrical current.

6.1.1. Volt

A technical definition of a volt is a unit of electrical potential difference or the potential difference across a conductor when a current of one ampere dissipates one watt of power. In water terminology, voltage is represented by the pressure that is the water supply tank. This is a potential because unless you provide an exit path for water to leave the tank, this potential is not realized. If you increase the pressure in the tank, you increase the potential to supply water or power.

6.1.2. Ohm

An ohm is a measure of resistance or electrical impedance. When comparing electricity with water, resistance is determined by the size or diameter of the hose or pipe that is used to supply water, where a smaller hose produces more resistance.

6.1.3. Amp

An ampere (amp) is a unit of electric current or the measure of electrical flow. When referring to water, it is also the rate of water flow. There is a direct relationship between volts, resistance, and current: If you reduce resistance or increase voltage, you increase the current. This relationship — Ohm's ...