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### Theory:

Electric current or simply current ($$I$$) is the rate at which charges flow past a point on a circuit.

Flow of charges in a wire

The value of current can be measured and expressed numerically. The SI unit for current is the ampere, and it is denoted as '$$A$$'. The formula is given as,

Where '$$I$$' is current, '$$t$$' is the time and '$$q$$' is the amount of charge flowing through the cross-section of a wire in time ($$t$$).
One ampere ($$1\ A$$) is defined as one coulomb ($$1\ C$$) of charge passing through a cross-section of a wire every one second ($$1\ s$$).
Mathematically,

Other units of ampere:
There are some other units of ampere listed in the table below.

 Units Symbols In ampere kiloampere $$kA$$ $$10^3 A$$ Megaampere $$MA$$ $$10^6 A$$ milliampere $$mA$$ $$10^{-3} A$$ microampere $$\mu A$$ $$10^{-6} A$$
Measuring device:
An ammeter is a device that measures the strength of the electric current in an electric circuit.
An ammeter

Ammeter is always connected in series in a circuit. The current enters the ammeter by the positive ($$+$$) red terminal and exits through the negative ($$–$$) black terminal.

Ammeter connection in a circuit with diagram