The Ampere

One of the simplest (though not actually the official) definitions of an ampere (amp) is 1 coulomb of charge carriers passing through a given location per second.

One coulomb is equal to 6.242 x10^18 (6,242,000,000,000,000,000,000) charge carriers. A fantastically large number, but given the relative size of electrons, one can imagine that number of charges moving on a relatively modest wire. Consider household wiring, which is typically 14 or 12 gauge, and rated at carrying 10 or 15 amps (at 120 volts), respectively.

Amperage == Current

Amperage is often referred to as current.

Common Amperages

To get an idea of the amount of work that can be done with that number of electrons, consider the following household appliances and their amperage:

Appliance Amperage
60 Watt incandescent light bulb 500mA (0.5A)
10 Watt LED (60 Watt incandescent equivalent) ~100mA (0.1A)
Hair Dryer 12 amps
Amp Hours (Ah)

When describing the quantity of charge either available, or used, amp hours (Ah), are used. An amp hour is an hour’s worth of amps, or 3,600 coulombs (since there are 3,600 seconds in an hour).

In our water tower analogy, the quantity of water flowing over our water wheel at any given second is measured in amps, and the quantity of water stored in the water tower (battery), is described in amp hours.

Amp hours are often expressed in milliampere hours (mAh), which is one-thousandth of an amp hour, or 3.6 coulombs. For reference, a typical AA NiMH rechargeable battery will have ~2500 mAh (2.5Ah), and a D NiMH rechargeable has ~10,000 mAh (10 Ah).

Next - Voltage


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