Ampere

Current is a measure of the rate at which the charge carriers flow. The standard unit of it is ampere. This represents 1 coulomb (6,240,000,000,000,000,000) of charge carriers per second for a given point.

An ampere is a comparatively large amount of current. The abbreviation is A. Current can be specified in terms of milliamperes, abbreviated μA, here 1 μA = 0.001 A or a thousand^th of an ampere. You will at times hear of microamperes (µA), here 1 µA 0.000001 A = 001 mA, a millionth of an ampere. And it is increasingly common to hear about nanoamperes, where 1 nA=0. 001 µA=0.000000001 A. Rarely will you hear of kiloamperes, where 1 kA=1000 A.

A current of a few milliamperes will give you a startling shock. Around 50 mA will severely jolt you, and 100 mA can even cause death if it flows through your chest cavity.

A 100-watt light bulb draws about 1 A of current. An electric iron draws around 10 A; a household uses between 10 A and 50 A, depending on the size of the house and the types of appliances it has, and on the time of day, week or year.

The amount of current which will flow in an electrical circuit is dependent on the voltage, and on the resistance. There are some circuits in which extremely large currents, around 1000 A, flow; this can happen through a metal bar placed directly at the output of a massive electric generator. The resistance is extremely low in this case, and the generator is capable of driving large amounts of charge. In some of the semiconductor electronic devices, like microcomputers, a few nanoamperes  will suffice for many complicated processes. Some electronic clocks draw so less current that their batteries last as long as they would if left on the shelf without being put to any use.