Unit-1 DC Circuit PDF

Basic Electrical Engineering What is Electric It consists of three basic components: a battery, a Circuit? lamp, and connecting wires. Such a simple circuit can exist by itself; it has several applications, such as a torch light, a search...

Basic Electrical Engineering What is Electric It consists of three basic components: a battery, a Circuit? lamp, and connecting wires. Such a simple circuit can exist by itself; it has several applications, such as a torch light, a search light, and so forth. CHARGE AND CURRENT The most basic quantity in an electric circuit is the electric charge.  It is conventional to take the current flow as the movement of positive charges, that is, opposite to the flow of negative charges, as Fig. 1.3 illustrates. This convention was introduced by Benjamin Franklin (1706–1790), the American scientist and inventor. Although we now know that current in metallic conductors is due to negatively charged electrons, we will follow the universally accepted convention that current is the net flow of positive charges. Thus, Direct Current If the current does not change with time, but remains constant, we call it a direct current (dc). Alternating Current  Once we define current as the movement of charge, we expect current to have an associated direction of flow. As mentioned earlier, the direction of current flow is conventionally taken as the direction of positive charge movement. Based on this convention, a current of 5 A may be represented positively or negatively as shown in Figure. In other words, a negative current of −5 A flowing in one direction as shown in Figure is the same as a current of +5 A flowing in the opposite direction. Voltage To move the electron in a conductor in a particular direction requires some work or energy transfer. This work is performed by an external electromotive force (emf), typically represented by the battery in above discussed Figure. This emf is also known as voltage or potential difference. The voltage vab between two points a and b in an electric circuit is the energy (or work) needed to move a unit charge from a to b; mathematically, CIRCUIT ELEMENTS There are two types of elements found in electric circuits: passive elements and active elements. An active element can generate energy while a passive element is not. Examples of passive elements are resistors, capacitors, and inductors. Typical active elements include generators, batteries, and operational amplifiers.  Practical Sources Practical voltage and current sources are not ideal, due to their internal resistances or source resistances and They become ideal a Rs and Rp. To show that this is the case, consider the effect of the load on voltage sources. The control of the dependent source is achieved by a voltage or current of some other element in the circuit, and the source can be voltage or current, it follows that there are four possible types of dependent sources, namely: It should be noted that an ideal voltage source (dependent or independent) will produce any current required to ensure that the terminal voltage is as stated, whereas an ideal current source will produce the necessary voltage to ensure the stated current flow. Thus, an ideal source could in theory supply an infinite amount of energy. It should also be noted that not only do sources supply power to a circuit, but they can also absorb power from a circuit too. For a voltage source, we know the voltage but not the current supplied or drawn by it. By the same token, we know the current supplied by a current source but not the voltage across it. Kirchhoff’s Laws Ohm’s law by itself is not sufficient to analyze circuits. However, when it is coupled with Kirchhoff’s two laws, we have a sufficient, powerful set of tools for analyzing a large variety of electric circuits. Resistance  A resistor that obeys Ohm’s law is known as a linear resistor. A nonlinear resistor does not obey Ohm’s law. Question  A useful quantity in circuit analysis is the reciprocal of resistance R, known as conductance and denoted by G: The conductance is a measure of how well an element will conduct electric current. Inductance The terms coil and choke are also used for inductors.  If current is allowed to pass through an inductor, it is found that the voltage across the inductor is directly proportional to the time rate of change of the current. Capacitance where A is the surf ace area of each plate, d is the distance between the plates, and ϵ is the permittivity of the dielectric material between the plates. Power and Energy For practical purposes, we need to know how much power an electric device can handle. instantaneous power. In fact, the law of conservation of energy must be obeyed in any electric circuit. For this reason, the algebraic sum of power in a circuit, at any instant of time, must be zero:  The power delivered to the inductor is Series Circuit Two elements are in series if Disadvantage of series circuit  If any break takes place at any point in a circuit, there will not be any current flow.  High Voltage cannot be connected by this method.  Not practicable for residential wirings.  Operation is not efficient. Voltage Divider Rule Parallel Circuits CURRENT DIVIDER RULE Star Delta Conversion Source Transformation Series-parallel combination and wye-delta transformation help simplify circuits. Source transformation is another tool for simplifying circuits. Superposition Thevenin’s Theorem Norton Theorem Numerical Numerical Category 2 Numerical Numerical