EE201 Fundamentals of Electric Circuits

by

Dr. Ibraheem Nasiruddin

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WHEEL-2

Connect / AttendConnect: Group ActivityAsk the students to form groups randomly in the class to hold their neighbors hand and only two students have their one hand unoccupied in the group?Identify one of the unoccupied hand as input and provide eatables and ask them to pass on or consume it ?Collect the eatable from last unoccupied hand as output.

Attend: • Listen individual Responses after observation by them

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conclude connect and attend activity and compile thoughts conclude connect and attend activity and compile thoughts Ask them to list down their observation based on the discussionAsk them to list down their observation based on the discussion List down various properties to identify electrical elementsList down various properties to identify electrical elements

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BASIC PARAMETERS AND SIMPLE RESISTIVE CIRCUITS

Mind Map

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TANETWORK

Simple Resistive Circuits

Basic Concepts

Current

Voltage

ResistanceOhm's Law

Power

Energy

Series Circuits and KVL

Parallel Circuits and KCL

Series-Parallel Network

The Electric Current

• The free electron is the charge carrier in a copper wire or any other solid conductor of electricity.

• With no external forces applied, the net flow of charge in a conductor in any one direction is zero.

Basic Electric Circuit

• To create the simplest of electric circuits. The battery, at the expense of chemical energy, places a net positive charge at one terminal

and a net negative charge on the other. • The instant the final connection is made, the free electrons

(of negative charge) will drift toward the positive terminal, while the positive ions left behind in the copper wire will simply oscillate in a mean fixed position.

• The negative terminal is a “supply” of electrons to be drawn from, while the electrons of the copper wire drift toward the positive terminal.

• The flow of charge (electrons) through the bulb will heat up the filament of the bulb through friction to the point that it will glow red hot and emit the desired light.

• A coulomb (C) of charge was defined as the total charge associated with 6.242x1018 electrons. The charge associated with one electron can then be determined from

Potential Difference• In the battery, the internal chemical action will establish

(through an expenditure of energy) an accumulation of negative charges (electrons) on one terminal (the negative terminal) and positive charges (positive ions) on the other (the positive terminal).

• A “positioning” of the charges has been established that will result in a potential difference between the terminals. If a conductor is connected between the terminals of the battery, the electrons at the negative terminal have sufficient potential energy to overcome collisions with other particles in the conductor and the repulsion from similar charges to reach the positive terminal to which they are attracted.

• A potential difference of 1 volt (V) exists between two points if 1 joule (J) of energy is exchanged in moving 1 coulomb (C) of charge between the two points.

Conductors and Insulators

The Resistor

SI Prefixes

SUPERCONDUCTORS• Superconductors are conductors of electric charge that, for all practical

purposes, have zero resistance.

TYPES OF RESISTORS

• Fixed Resistors

• Variable Resistors

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Series Resistor Circuits

Two elements are in series if1. They have only one terminal in common (i.e., one lead of one is connected to only one lead of the other).2. The common point between the two elements is not connected to another current-carrying element.The current is the same through series elements.

EXAMPLE Determine RT, I, and V2 for the circuit

VOLTAGE SOURCES IN SERIES

KIRCHHOFF’S VOLTAGE LAW• Kirchhoff’s voltage law (KVL) states that the algebraic

sum of the potential rises and drops around a closed loop (or path) is zero.

VOLTAGE DIVIDER RULE

• the voltage across the resistive elements will divide as the magnitude of the resistance levels.

INTERNAL RESISTANCEOF VOLTAGE SOURCES

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Parallel Resistors Circuits

• Two elements, branches, or networks are in parallel if they have two points in common as shown

TOTAL CONDUCTANCE AND RESISTANCE

PARALLEL CIRCUITS

KIRCHHOFF’S CURRENT LAW

CURRENT DIVIDER RULEThe current divider rule (CDR) will determine how the current entering a set of parallel branches will split between the elements.For two parallel elements of equal value, the current will divide equally. For two parallel elements with different values, the smaller the resistance, the greater the share of input current with a ratio equal to the inverse of their resistor values.

Example

Two Examples

Determine the resistance R1 to effect the division of current.

Solve for R1

VOLTAGE SOURCES IN PARALLELVoltage sources are placed in parallel as shown in the Figure only if they have the same voltage rating. The primary reason for placing two or more batteries in parallel of the same terminal voltage would be to increase the current rating (and, therefore, the power rating) of the source. The current rating of the combination is determined by Is= I1 + I2 at the same terminal voltage. The resulting power rating is twice that available with one supply.

OPEN AND SHORT CIRCUITSAn open circuit can have a potential difference (voltage) across its terminals, but the current is always zero amperes.A short circuit can carry a current of a level determined by the external circuit, but the potential difference (voltage) across its terminals is always zero volts.

SERIES-PARALLEL NETWORKSseries-parallel networks are networks that contain both series andparallel circuit configurations.Examine each region of the network independently before tying them together in series-parallel combinations. This will usually simplify the network and possibly reveal a direct approach toward obtaining one or more desired unknowns. It also eliminates many of the errors that might result due to the lack of a systematic approach.Redraw the network as often as possible with the reduced branches and undisturbed unknown quantities to maintain clarity and provide the reduced networks for the trip back to unknown quantities from the source.

Reduce and Return Approach

For many single-source, series-parallel networks, the analysis is one that works back to the source, determines the source current, and then finds its way to the desired unknown. In the shown Fig., for instance, thevoltage V4 is desired.

Block Diagram Approach

There will be some concern about identifying series and parallel elements and branches and choosing the best procedure to follow toward a solution.In the above Fig., blocks B and C are in parallel (points b and c in common), and the voltage source E is in series with block A (point a in common). The parallel combination of B and C is also in series with A and the voltage source E due to the common points b and c, respectively.The following notation will be used for series and parallel combinations of elements. For series resistors R1 and R2, a comma will be inserted between their subscript notations, as shown here:

For parallel resistors R1 and R2, the parallel symbol will be inserted between their subscript notations, as follows:

Example

Example

Example

ExampleNote that the unknown voltages do not have to be across elements but can exist between any two points in a network.In addition, the importance of redrawing the network in a morefamiliar form is clearly revealed by the analysis to follow.Find the voltages V1, V3, and Vab for the shown network and Calculate the source current Is.Using the voltage divider rule to determine V1 and V3.The open-circuit voltage Vab is determined by applying Kirchhoff’s voltage law around the indicated loop of the shown Fig. in the clockwisedirection starting at terminal a.

ExampleDetermine the voltages V1 and V2 and the current I.It would indeed be difficult to analyze the network in its original form with the symbolic notation for the sources and the reference or ground connection in the upper left-hand corner of the diagram.However, when the network is redrawn as shown, the unknowns and the relationship between branches become significantly clearer.It is now obvious that V2 = - E1 = - 6 VApplying Kirchhoff’s voltage law to the loop indicated, we obtain: -E1 + V1 - E2 = 0

LADDER NETWORKSThe reason for the terminology is quite obvious for the repetitive structure. Basically two approaches are used to solve networks of this type.

•Method 1: Calculate the total resistance and resulting source current, and then work back through the ladder until the desired current or voltage is obtained.•Method 2: Assign a letter symbol to the last branch current and work back through the network to the source, maintaining this assigned current or other current of interest. The desired current can then be found directly.

Method 1 Method 2

CURRENT SOURCESThe current source is often referred to as the dual of the voltage source. •A battery supplies a fixed voltage, and the source current can vary; but the current source supplies a fixed current to the branch in which it is located, while its terminal voltage may vary as determined by the network to which it is applied. •Note from the above that duality simply implies an interchange of current and voltage to distinguish the characteristics of one source from the other. •In the basic electronics courses, the transistor is a current-controlled device. In the equivalent circuit of a transistor used in the analysis of transistor networks, there appears a current source as shown. •The symbol for a current source appears in the same Fig. The direction of the figure. The arrow direction within the circle indicates the direction in which current is being supplied.

Examples

CURRENT SOURCES IN PARALLELIf two or more current sources are in parallel,

they may all be replacedby one current source having the magnitude and direction of the resultant current.

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