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TEXT A
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In the same way as water flows from a point of high potential energy to a
point of low potential energy (i.e. from full to empty), so the electric current
flows from a high-potential (excess of electrons) to a low-potential point
(deficiency of electrons). The current may flow through solid conductors,
liquids, gases, a vacuum or any combinations of these and that path of the
electric current is called the electric circuit.
The simplest electric circuit contains only three parts, i.e. one load, one
voltage source, and one control device. Most complete electric circuits contain
six parts:
1. an energy source to provide the voltage needed to force current
(electrons) through the circuit,
2. conductors through which the current can travel,
3. insulators to confine the current to the desired paths,
4. a load to control the amount of current and convert the electric energy
taken from the energy source
5. a control device, often a switch, to start and stop the flow of current
and
6. a protection device to interrupt the circuit in case of a circuit
malfunction.
Examples of energy sources are dry cells, accumulators, or generators.
Conductors are wires, cables, or other bodies or medium suitable for carrying
electric current. An insulator is a device that has high electric resistance, for
supporting or separating conductors to prevent undesired flow of current from
the conductors to other objects. A load is a device that consumes electric power,
e.g. lamps, motors, household appliances etc. A control device, often a switch,
is used to start or stop the flow of current. A protective device, i.e. a fuse, which
is inserted in series with the circuit being protected, opens the circuit
automatically during a serious overload.
These devices, as well as conductors, offer some resistance to the current.
It may be high or low and depends on the type of the circuit and the kind of
load that has been used. We have already learned what the resistance of a
conductor depends on, so now several general types of circuits and their
schematic diagrams will be considered.
Basic types of circuits differed by the type of the connection are a series
circuit, a parallel circuit, and a complex circuit (e.g. series parallel circuit).
