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There two ways to connect elements in a circuit: series and parallel. In a series circuit, the overall resistance is the sum of all the resistance in the circuit and in a parallel setting it is equal to the the reciprocal of the sum of the reciprocal of all resistances in the circuit.
The rate of energy (doing work) over time is called power. Therefore, the integral of power over time results in the work done by the energy. The energy to do work is supplied by the voltage or the current source in a circuit. This work shows itself as heat in the resistors. Basically as the current flows, the resistors resist the flow, and the energy stored in the current by the source converts into heat at the resistors to overcome the resistance and continue the flow in the circuit and this work results in a drop of voltage (source of energy).
In DC circuits, current and voltage do not change by time and they are shown by I and V. According to Joule's law, in a circuit with a drop of voltage between two terminals V, current I, and total resistance R, the power P = VI = V2/R = I2R.
In simple words, an electrical circuit is a path that electrons flow in it. This flow of electron which is a result of difference in charge (electrical energy) of two points, is called electrical current. The source of the current can be active or passive element: Active elements such as the voltage or current source can generate electrical energy; Passive elements can store energy by absorbing it such as capacitors or inductors. There are some passive elements that dissipate energy such as resistors. Capacitors are made of two conductor surfaces with an insulator in between (e.g. parallel plate capacitor).
A voltage source is ideal if it generates constant voltage no matter how much the current is. Similarly, an ideal current source is created power at a constant current no matter how much is difference in voltage between the two end of it. But these are just in an ideal world. In reality, when current increases, voltage source cannot keep generating a constant voltage because if their internal resistance. If the sources of current and voltage work according to what is going on the circuit (i.e. decrease and increase in current or voltage) their are called dependent sources, otherwise they are called independent. As we already know from electrostatics, the potential difference between the terminals of a circuit is called voltage, which is measured by units of volts (also W/A, C/F, J/C, A/S, and Wb/s). Basically, any devise that generates electrical energy is called a seat and is measured in volts.
Circuit elements have resistance (R) against the flow of current, which is measured in units of ohm (Ω) that is named after German physicist Georg Simon Ohm. If a circuit has zero resistance, it is called short circuit and if the resistance is infinite, it is called open circuit. The property out of which the resistance are made have different resistivity (ρ measured in Ω.m). Resistivity of a material in addition to its length and cross section give the material its resistance (R = ρL/A). Resistivity of conductors usually increases with temperature and decreases for semi-conductors. How temperature affects the resistivity is shown by thermal coefficient of resistance, α.
Capacitors are two conductors with an insulator in between. When they are connected to a voltage potential, the charges Q, will be stored inside the insulator, which is proportional to the voltage and capacitance, C measured in farads, (F): Q = CV. One also needs to know about the capacitance, current and voltage in capacitor, and the total energy stored in a capacitor. The equivalent capacitance of several capacitor in series and parallel setting is important to know.Inductors are a coil of wire and when they are connected to voltage potential they create a magnetic field that opposes the current changes. The equivalent inductance of several inductors in series and parallel setting is important to know.
The circuit analyses is discussed in another page.
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