Basic Concepts and Basic Laws

Chapter 1 & 2 Study Notes

Chapter 1: Basic Concepts

• Electric Circuit Theory and Electromagnetic Theory are the two fundamental theories of electrical engineering [1].

• Many branches of electrical engineering, such as power, electric machines, control, electronics, communications and instrumentation are built on electric circuit theory [1].

• An electric circuit is an interconnection of electrical elements [2].

• The goal of circuit analysis is to learn analytical techniques and computer software applications for describing the behaviour of a circuit [3].

• The International System of Units (SI) is the international measurement language used by engineers [4].

• See Table 1.1 [3] and Table 1.2 [5] for a list of common units and prefixes used in electrical engineering.

• Charge is the most basic quantity in an electric circuit [6].

• The unit of charge is the coulomb (C) [7].

• The charge of an electron is -1.602 x 10-19 C [8].

• The law of conservation of charge states that charge can neither be created nor destroyed, only transferred [7].

• Electric current is the flow of electric charges [9].

• The unit of current is the ampere (A), which is equal to one coulomb per second [10].

• Direct current (DC) is a current that remains constant with time [11].

• Alternating current (AC) is a current that varies sinusoidally with time [11].

• Voltage (or potential difference) is the energy required to move a unit charge through an element [12].

• The unit of voltage is the volt (V) [12].

• A voltage drop from point a to point b is equivalent to a voltage rise from point b to point a [13].

• Power is the time rate of expending or absorbing energy [14].

• The unit of power is the watt (W) [14].

• The passive sign convention is used to determine the sign of power [15].

• If the power has a positive sign, power is being absorbed by the element.

• If the power has a negative sign, power is being supplied by the element.

• Energy is the capacity to do work [16].

• The unit of energy is the joule (J) [16].

• Electric power utility companies measure energy in watt-hours (Wh), where 1 Wh = 3,600 J [16].

• Passive elements, such as resistors, capacitors, and inductors, are not capable of generating energy [17].

• Active elements, such as generators, batteries, and operational amplifiers, are capable of generating energy [17].

• Voltage and current sources can be either independent or dependent [18].

• An independent source provides a specified voltage or current that is not affected by other circuit elements [18].

• A dependent (or controlled) source provides a voltage or current that is controlled by another voltage or current in the circuit [19].

Chapter 2: Basic Laws

• Resistance is the ability of a material to resist the flow of electric current [20].

• The unit of resistance is the ohm (Ω) [21].

• Ohm's Law states that the voltage v across a resistor is directly proportional to the current i flowing through it [22].

• v = iR [23]

• A short circuit is a circuit element with zero resistance (R = 0) [24].

• A short circuit has zero voltage across it, regardless of the current flowing through it [24].

• An open circuit is a circuit element with resistance approaching infinity [24].

• An open circuit has zero current flowing through it, regardless of the voltage across it [24].

• Conductance is the reciprocal of resistance, and is a measure of how easily an element will conduct current [25].

• The unit of conductance is the siemens (S), which is equal to one reciprocal ohm [26].

• G = 1/R = i/v [71, 72, 2.9].

• Kirchhoff's Current Law (KCL) states that the algebraic sum of currents entering a node is zero [27].

• Kirchhoff's Voltage Law (KVL) states that the algebraic sum of voltages around a closed path is zero [28].

• Series circuits:

• Elements in series carry the same current [29].

• The total resistance of a series circuit is the sum of the individual resistances [30].

• Voltage division is used to determine the voltage across each resistor in a series circuit [31].

• Parallel circuits:

• Elements in parallel have the same voltage across them [29].

• The total resistance of a parallel circuit is less than the resistance of the smallest individual resistor [32].

• Current division is used to determine the current through each resistor in a parallel circuit [32].

• Wye (Y) and Delta (Δ) Networks are three-terminal equivalent networks that can be used to simplify circuits that are neither in parallel nor in series [33].

• Delta-to-wye conversion: each resistor in the Y network is the product of the resistors in the two adjacent Δ branches, divided by the sum of the three Δ resistors [34].

• Wye-to-delta conversion: each resistor in the Δ network is the sum of all possible products of Y resistors taken two at a time, divided by the opposite Y resistor [35].

This response is based solely on the information provided in the sources.