Basic Engineering

Source Transformation :  In an electric circuit, it is often convenient to have a voltage source rather than a current source (e.g. in mesh analysis) or vice versa. This is made possible using source transformations. It should be noted that only practical voltage and current sources can be transformed. In other words, a Th´evenin’s equivalent circuit is transformed into a Norton’s one or vice versa. The parameters used in the source transformation are given as follows. Any load resistance, RL will have the same voltage across, and current through it when connected across the terminals of either source. Example:  In given figure, use repeated source transformation to determine the current through the5Ωresistance. Noting that the voltage source and the 10 Ω resistor are in series, transform the combination into a current source in parallel with the 10 Ω resistor. The magnitude of the current source is calculated as follows        ...

DC Sources:  In general, there are two main types of DC sources  Independent (Voltage and Current) Sources  Dependent (Voltage and Current) Sources An independent source produces its own voltage and current through some chemical reaction and does not depend on any other voltage or current variable in the circuit. The output of a dependent source, on the other hand, is subject to a certain parameter (voltage or current) change in a circuit element. Herein, the discussion shall be confined to independent sources only. DC Voltage Source:  This can be further subcategorised into ideal and non-ideal sources. The Ideal Voltage Source An ideal voltage source, shown in Figure (a), has a terminal voltage which is independent of the variations in load. In other words, for an ideal voltage source, the supply current alters with changes in load but the terminal voltage, VL always remains constant. This characteristic is depicted in given figure(b). Non-Ideal or P...

Branch current method: The first and most straightforward network analysis technique is called the  Branch Current Method . In this method, we assume directions of currents in a network, then write equations describing their relationships to each other through Kirchhoff's and Ohm's Laws. Once we have one equation for every unknown current, we can solve the simultaneous equations and determine all currents, and therefore all voltage drops in the network. Let's use this circuit to illustrate the method: The first step is to choose a node (junction of wires) in the circuit to use as a point of reference for our unknown currents. I'll choose the node joining the right of R 1 , the top of R 2 , and the left of R 3 . At this node, guess which directions the three wires' currents take, labeling the three currents as I 1 , I 2 , and I 3 , respectively. Bear in mind that these directions of current are speculative at this point. Fortunately, if it turns out ...

Thevenin's Theorem: Thevenin's Theorem states that it is possible to simplify any linear circuit, no matter how complex, to an equivalent circuit with just a single voltage source and series resistance connected to a load. The qualification of "linear" is identical to that found in the Superposition Theorem, where all the underlying equations must be linear (no exponents or roots). If we're dealing with passive components (such as resistors, and later, inductors and capacitors), this is true. However, there are some components (especially certain gas-discharge and semiconductor components) which are nonlinear: that is, their opposition to current  changes  with voltage and/or current. As such, we would call circuits containing these types of components,  nonlinear circuits . Thevenin's Theorem is especially useful in analyzing power systems and other circuits where one particular resistor in the circuit (called the "load" resistor) is subject t...

Polarity of voltage drops:    We can trace the direction that electrons will flow in the same circuit by starting at the negative (-) terminal and following through to the positive ( ) terminal of the battery, the only source of voltage in the circuit. From this we can see that the electrons are moving counter-clockwise, from point 6 to 5 to 4 to 3 to 2 to 1 and back to 6 again. As the current encounters the 5 Ω resistance, voltage is dropped across the resistor's ends. The polarity of this voltage drop is negative (-) at point 4 with respect to positive ( ) at point 3. We can mark the polarity of the resistor's voltage drop with these negative and positive symbols, in accordance with the direction of current (whichever end of the resistor the current is  entering  is negative with respect to the end of the resistor it is  exiting : We could make our table of voltages a little more complete by marking the polarity of the voltage for each pair of poin...

Conventional versus electron flow: we tend to associate the word "positive" with "surplus" and "negative" with "deficiency," the standard label for electron charge does seem backward. Because of this, many engineers decided to retain the old concept of electricity with "positive" referring to a surplus of charge, and label charge flow (current) accordingly. This became known as  conventional flow notation: Others chose to designate charge flow according to the actual motion of electrons in a circuit. This form of symbology became known as  electron flow  notation: In conventional flow notation, we show the motion of charge according to the (technically incorrect) labels of and -. This way the labels make sense, but the direction of charge flow is incorrect. In electron flow notation, we follow the actual motion of electrons in the circuit, but the and - labels seem backward.

passive element:   The element which receives energy (or absorbs energy) and then either converts it into heat (R) or stored it  in an electric (C) or magnetic (L ) field is called passive element.  Active element:   The elements that supply energy to the circuit is called active element. Examples of active elements include voltage and current sources, generators, and electronic devices that require power supplies. A transistor is an active circuit element, meaning that it can amplify power of a signal. On the other hand, transformer is not an active element because it does not amplify the power level and power remains same both in primary and secondary sides. Transformer is an example of passive element