Текст ELECTRIC CIRCUIT
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ELECTRIC CIRCUIT
The circuit is known to be a complete path which carries the current from the source of supply to the load and then carries it again from the load back to the source.
The purpose of the electrical source is to produce the necessary electromotive force required for the flow of current through the circuit.
The path along which the electrons travel must be complete otherwise no electric power can be supplied from the source to the load. The circuit is closed when an electric lamp is switched on.
If the circuit is broken or, «opened» anywhere, the current is known to stop everywhere. The circuit is broken when electrical devices are switched off. Generally speaking, the current may pass through solid conductors, liquids, gases, vacuum, or any combination of these. It may flow in turn over transmission lines
from the power-stations through transformers, cables and switches, through lamps, heaters, motors and so on.
There are various kinds of electric circuits such as: open circuits, closed circuits, series circuits, parallel circuits and short circuits.
To understand the difference between the following circuit connections is not difficult at all. When electrical devices are connected so that the current flows from one device to another, they are said to be connected in series. Under such conditions the current flow is the same in all parts of the circuit, as there is only a single path along which it may flow. The electrical bell circuit is considered to be a typical example of a series circuit.
The parallel circuit provides two or more paths for the passage of current. The circuit is divided in such a way that part of the current flows through one path, and part through another. The lamps in a room are generally connected in parallel.
The short circuit is produced when the current is allowed to return to the source of supply without control and without doing the work that is wanted to do. The short circuit often results from cable fault or wire fault. Under certain conditions, the short may cause fire because the current flows where it was not supposed to flow. If the current flow is too great a fuse is to be used as a safety device to stop the current flow.
The fuse must be placed in every circuit where there is a danger of overloading the line. Then all the current to be sent will pass through the fuse.
When a short circuit or an overload causes more current to flow than the carrying capacity of the wire, the wire becomes hot and sets fire to the insulation. If the flow of current is greater than the carrying capacity of the fuse, the fuse melts and opens the circuit.