The SI unit of electric current is the Ampere, symbolized by the letter A. Electric current measures the flow of electric charge through a conductor. The Ampere is one of the seven base units in the International System of Units, and it's named after the French physicist André-Marie Ampère. Current is calculated as charge divided by time.
The ampere has a precise scientific definition based on electromagnetic force. According to the SI definition, one ampere is the constant current that, when flowing through two parallel conductors one meter apart, produces a force of exactly 2 times 10 to the minus 7 newtons per meter of length. In practical terms, one ampere equals one coulomb of electric charge passing through a cross-section in one second.
Electric current varies dramatically in everyday applications. A small LED uses only 20 milliamperes, while a smartphone charger typically draws 1 to 2 amperes. Household appliances like light bulbs use around half an ampere, while electric kettles require 10 to 15 amperes. Car starter motors need hundreds of amperes, and lightning bolts can reach tens of thousands of amperes. We use prefixes like milli, micro, and kilo to express these different scales conveniently.
To measure electric current, we use an instrument called an ammeter or a multimeter set to current mode. The key principle is that current must flow through the measuring device, so we connect the ammeter in series with the circuit. This means we break the circuit at the point where we want to measure current and insert the ammeter. Safety is crucial when measuring current - always start with the highest range setting, never connect an ammeter in parallel, and turn off power before making connections.
To summarize what we have learned: The SI unit of electric current is the Ampere, symbolized by A. It is named after the French physicist André-Marie Ampère and is precisely defined based on electromagnetic force between parallel conductors. Current represents the flow of electric charge and is calculated as charge divided by time. Current values in practical applications range from tiny microamperes in electronic devices to thousands of amperes in industrial equipment. We measure current using ammeters that must be connected in series with the circuit.