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CompTIA A+ Certification All-in-One Exam Guide

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Figure 7-2 Electrical voltage as water pressure

The amount of electrons moving past a certain point on a wire is called the

current (or amperage), which is measured in units called amperes (amps or

A). See Figure 7-3.

Figure 7-3 Electrical amperage as amount of water flowing

The amps and volts needed so that a particular device will function is

expressed as how much wattage (watts or W) that device needs. The

correlation between the three is very simple math: V × A = W. You’ll learn

more about wattage a little later in this chapter.

Wires of all sorts—whether copper, tin, gold, or platinum—have a slight

resistance to the flow of electrons, just as water pipes have a slight amount of

friction that resists the flow of water. Resistance to the flow of electrons is

measured in ohms (Ω).

• Pressure = voltage (V)

• Volume flowing = amperes (A)

• Work = wattage (W)

• Resistance = ohms (Ω)

A particular thickness of wire only handles so much current at a time. If

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