http://www.ck12.org Chapter 17. Circuits
Electric Current
An electric current is a flow of charges under the influence of an electric field. A flow of charges can be established,
for instance, between the terminals of a battery, as inFigure17.2. The rateI=∆∆Qt at which charges flow within a
conducting wire past any point in the wire is defined as the electric current.
The unit of current iscoulombssecond which is called theampereoramp(named for the French physicist Andre’-Marie
Ampere, 1775-1836),Figure17.3.
The symbolAis used to represent the ampere. A rate of one coulomb per second is equivalent to one ampere:
1 C
1 s=^1 A
FIGURE 17.2
Figure 17.2 shows a flow of electrons (e^-) from the positive terminal of a battery through a light bulb to the negative
terminal of a battery.
FIGURE 17.3
Andre’-Marie AmpereOne ampere is a very large current. The current of 1 A can easily kill a person. In fact, about 0.20 A can kill rather
easily. Even relatively small voltage can produce these currents, which is why care must always be taken when
dealing with all electrical appliances and any electrical device that is plugged into a wall outlet. A typical 12-V
car battery can also be dangerous. Under the right circumstances, it does not take a huge voltage to cause deadly
currents.
It is common to express current in milliamperes 1 mA= 10 −^3 A, or microamperes 1 ̄A= 10 −^6 A.