In the real life and production of various circuit is made up of a variety of practical circuit components or equipment, such as shown below in the circuit, the circuit is made up of dry battery, switch, light bulbs and number of wires, conform to form circuit three parts (power supply, load, and the intermediate links) , battery as a power source to provide power to the load, the light bulb as load electric energy into light energy absorption, the intermediate links are made up of wires and switches can control on-off circuit and current role. These batteries, light bulbs, switches and wires is that they are real element, the original electromagnetic phenomenon occurs in the work is not a single.
Such as electric bulb when it will not only heat, also can produce a weak magnetic field; Not only the coil current will produce magnetic field, coil will be fever; The resistance of the conductor is always there. So the actual circuit is a variety of electromagnetic phenomena are intertwined. But we have to study the problem of convenient, seize the main road and the secondary contradictions, the actual electrical components by the electromagnetic properties of single idealized components.
For example, in the case of mains frequency is not high, all kinds of resistor, incandescent and rice cooker can use "resistance element". The inductance coil, its internal resistance is small, can suddenly road, inductance coil can be equivalent to a "inductive components". For all kinds of capacitor can be used "capacitive element".For these batteries, battery, etc the actual dc power supply can be used "ideal voltage source" and "resistance" series. If according to the above method is used in actual circuit diagram above all kinds of ideal components make up the circuit model, then using the circuit model and the electrical graphics symbol, thus get the electric diagram.
To summarize, the actual circuit is made up of the actual circuit element, if the actual electrical components are idealized can get ideal circuit element, called a circuit model of ideal circuit element composition, if use electric circuit model graphics symbol when they got the circuit diagram.
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