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Theory:

Electric current or simply current (\(I\)) is the rate at which charges flow past a point on a circuit.
 
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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,
Current = ChargeTimeI = Qt
 
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,
 
1ampere =1coulomb1second1A =1C1s=1Cs1
 
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.
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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.
 
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Ammeter connection in a circuit with diagram