Current:
Current can be defined as the motion of charge through a conducting material. The unit of current isAmpere whilst charge is measured in Coulombs.
Definition of an Ampere:
“The quantity of total charge that passes through an arbitrary cross section of a conducting material per unit second is defined as an Ampere.”Mathematically,
I=Q/t
or
Q=It
where,
Q is the symbol of charge measured in Coulombs (C),I is the current in amperes (A) and t is the time in seconds (s).
The current can also be defined as the rate of charge passing through a point in an electric circuit i.e.
I=dQ/dt
A constant current (also known as direct current or DC) is denoted by the symbol I whereas a time-
varying current (also known as alternating current or AC) is represented by the symbol i or i(t).
Current is always measured through a circuit element.
Figure 2.1 demonstrates the use of an ampere-meter or ammeter in series with a circuit element,
R,to measure the current through it.
Figure 2.1:An ammeter is connected in series to measure current,I, through the element,R.
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