In the previous lesson about electrostatics, we have known that a positive charge flows from a higher electric potential to a lower electric potential. If there is a potential different between two points, then the electric charges will move, so that electric current flows. Potential difference is generated by voltage sources (such as battery) which have two terminals, positive terminal (+) and negative terminal(-).
Before the electron was found by J.J. Thomson (1856-1940) in the 20th century, scientist had an agreement that electric current was the flow of positive charges from positive terminal to negative terminal. This assumption was called conventional current.
If the positive and negative terminals of a battery are connected to a wire, then electrons will flow from the negative terminal to the positive one. The amount of negative charges which flow through the wire is equal to that of the positive charge which flow in opposite direction. Therefore electron current is still defined as conventional current.
if the switch is closed, then the electric current will flow on the circuit and it will turn on the light bulb, otherwise the switch is opened, then there will not be any current flows in the circuit turn on the bulb. Thus, we can say that electric current flows only on a closed loop.
Electric current (I) is defined as the amount of charge (q) flowing through conductor every second (t).
The SI unit of current is Ampere (A), named after a French physics, Andre Marie Ampere (1775-1836).
The relationship between I, q, and t is mathematically formulated as follows :
I = q/t
Note : q = electric charge (coulomb, C)
I = electric current (ampere, A)
t = time interval (second, s)
The smaller units for electric current are mill ampere (mA) and microampere (µA)
1 mA = 10-3 , A = o,oo1 A
1µA = 10-6 , A = 0,000001 A
