BE 8255 BASIC ELECTRICAL ELECTRONICS AND MEASUREMENT ENGINEERING

BE 8255 -BASIC ELECTRICAL, ELECTRONICS AND MEASUREMENT ENGINEERING By N. Rajagopalakrishnan, AP/ECE

BE 8255 BASIC ELECTRICAL, ELECTRONICS AND MEASUREMENT ENGINEERING UNIT I ELECTRICAL CIRCUITS ANALYSIS Ohms Law, Kirchhoff‘s Law-Instantaneous power- series and parallel circuit analysis with resistive, capacitive and inductive network - nodal analysis, mesh analysis- network theorems - Thevenins theorem, Norton theorem, maximum power transfer theorem and superposition theorem, three phase supply. Instantaneous, Reactive and apparent power-star delta conversion.

Electric Current • Electric current is the continuous flow of electric charge • Two types of current are direct and alternating • Direct current (DC) is when the charge flows in one direction • Alternating current (AC) is when the flow of electric charge regularly reverses direction

Electric Current • An example of a direct current is a flashlight and most battery-operated devices • Alternating current is in your home and school • Current is defined as the direction in which the positive charges would flow

Conductors and Insulators • An electrical conductor is a material through which charge can flow easily • Metals such as copper, and silver are good electrical conductors • An electrical insulator is a material through which charge cannot flow easily • Wood, plastic, rubber and air are good electrical insulators

Resistance • Resistance is the opposition to the flow of charges in a material • The SI unit of resistance is the ohm • A material’s thickness, length and temperature affect its resistance • Resistance is more in a longer wire • As temperature increases the resistance increases since the electrons collide more often

Resistance • A superconductor is a material that has almost zero resistance when it is cooled to low temperatures • Superconductors are trying to reduce the resistance to zero • The best superconductor has been cooled to 138 K

Voltage • In order for a charge to flow in a conducting wire, the wire must be connected in a complete loop that includes a source of electrical energy • A flashlight will not work if there is no battery

Potential Difference • Reminder potential energy is related to position • Charges flow from a high to low potential energy • Potential difference is the difference in electrical potential energy between two places in an electric field

Voltage Sources • Three common voltage sources are batteries, solar cells and generators • A battery is a device that converts chemical energy to electrical energy • In a 9 -volt battery the voltage drop is about 9 volts

Electricity Physical phenomenon arising from the existence and interactions of electric charge

Charge Characteristic property of subatomic particles responsible for electric phenomena Charge is the source of one of the fundamental forces in nature (others? ) Electron - + − 1. 602× 10− 19 C Proton The unit of electric charge is coloumb (C) 1 coloumb = 6. 25 × 1018 e e = elementary charge = charge of proton

Charge “Charged” particles exhibit forces - - Like charges repel each other - + Opposite charges attract one another

ATOMS AND ATOMIC STRUCTURE Atom Nucleus Proton Neutron Electron

WHAT IS AN ATOM? o The smallest unit of an element. o Consists of a central nucleus surrounded by one or more electrons.

WHAT IS THE NUCLEUS? o The central part of an atom. o Composed of protons and neutrons. o Contains most of an atom's mass.

WHAT IS A PROTON? o Positively charged particle. o Found within an atomic nucleus.

WHAT IS A NEUTRON? o Uncharged particle. o Found within an atomic nucleus.

WHAT IS AN ELECTRON? o Negatively charged particle. o Located in shells that surround an atom's nucleus.

Electric current Moving electrons in a conductive material or moving ions IS called Current Describes charge in motion, the flow of charge is called current

Electric current An ampere (A) is the number of electrons having a total charge of 1 C moving through a given cross section in 1 s. As defined, current flows in direction of positive charge flow

Current • Symbol: I • Unit: Ampere

Current-Water Analogy

Voltage • Symbol: V • Unit: Volt – Potential difference across two terminals in a circuit “across variable. ” – In order to move charge from point A to point B, work needs to be done.

Voltage-Water Analogy

NODES, BRANCHES, AND LOOPS: A branch is a single electrical element or device. Figure 4. 1: A circuit with 5 branches. A node: A node can be defined as a connection point between two or more branches. 2 Figure 4. 2: A circuit with 3 nodes.

Branch A branch is any portion of a circuit with two terminals connected to it. A branch may consist of one or more circuit elements. In practice, any circuit element with two terminals connected to it is a branch. Definition of a

Node A node is the junction of two or more branches (one often refers to the junction of only two branches as a trivial node). The figure below illustrates the concept. Definitions of node and

Loop Definition of a loop A loop is any closed connection of branches. Various loop configurations are illustrated below.

Mesh Definition of a mesh A mesh is a loop that does not contain other loops.

Series Connection of Cells • Each cell provides 1. 5 V • Two cells connected one after another, in series, provide 3 V, while three cells would provide 4. 5 V • Polarities matter

Parallel Connection of Cells • If the cells are connected in parallel, the voltage stays at 1. 5 V, but now a larger current can be drawn.

Wire-Water Analogy

Resistor Concept —I • Flow of electric current through a conductor experiences a certain amount of resistance. • The resistance, expressed in ohms ( , named after George ohm), kilo-ohms (k , 1000 ), or mega-ohms (M , 106 ) is a measure of how much a resistor resists the flow of electricity. • The magnitude of resistance is dictated by electric properties of the material and material geometry. • This behavior of materials is often used to control/limit electric current flow in circuits. • Henceforth, the conductors that exhibit the property of resisting current flow are called resistors. Resistor Symbols

Resistor Applications • Resistors are used for: – Limiting current in electric circuits. – Lowering voltage levels in electric circuits (using voltage divider). – As current provider. – As a sensor (e. g. , photoresistor detects light condition, thermistor detects temperature condition, strain gauge detects load condition, etc. ) – In electronic circuits, resistors are used as pull-up and pull-down elements to avoid floating signal levels.

Resistor Labels • Wire-wound resistors have a label indicating resistance and power ratings. • A majority of resistors have color bars to indicate their resistance magnitude. • There are usually 4 to 6 bands of color on a resistor. As shown in the figure below, the right most color bar indicates the resistor reliability, however, some resistor use this bar to indicate the tolerance. The color bar immediately left to the tolerance bar (C), indicates the multipliers (in tens). To the left of the multiplier bar are the digits, starting from the last digit to the first digit. Resistor value =

Resistor Color Codes Band color Digit Multiplier Black 0 X 1 Brown 1 X 10 Red 2 X 100 Color Tolerance Brown ± 1% Orange 3 X 1000 Red ± 2% Yellow 4 X 10000 Gold ± 5% Green 5 X 100000 Blue 6 X 1000000 Silver ± 10% violet 7 X 10000000 None ± 20% Grey 8 X 10000 White 9 X 100000 Silver - x. 01 Gold - x. 1

Example • • The first band is yellow, so the first digit is 4 The second band is violet, so the second digit is 7 The third band is red, so the multiplier is Resistor value is

Metric Units and Conversions Abbreviation Means p n µ m. k M G Multiply unit by pico. 0000001 nano. 00001 micro. 000001 milli. 001 Unit 1 kilo 1, 000 mega 1, 000 giga 1, 000, 000 Or 10 -12 10 -9 10 -6 10 -3 10 0 10 3 10 6 10 9

Digital Multimeter 1 • DMM is a measuring instrument • An ammeter measures current • A voltmeter measures the potential difference (voltage) between two points • An ohmmeter measures resistance • A multimeter combines these functions, and possibly some additional ones as well, into a single instrument

Ammeter Connection • Break the circuit so that the ammeter can be connected in series • All the current flowing in the circuit must pass through the ammeter • An ammeter must have a very LOW input impedance

Voltmeter Connection • The voltmeter is connected in parallel between two points of circuit • A voltmeter should have a very HIGH input impedance

Ohmmeter Connection • An ohmmeter does not function with a circuit connected to a power supply • Must take it out of the circuit altogether and test it separately

Resistors in Series Rtotal=R 1+R 2 Rtotal=1+1=2 kΩ

Resistors in Parallel

Exercise 1

Capacitor Concept • A capacitor is an energy storage element which is analogous to the spring element of mechanical systems. • It can store electrical pressure (voltage) for periods of time. -When a capacitor has a difference in voltage (electrical pressure) across its plate, it is said to be charged. -A capacitor is charged by having a one-way current flow through it for a period of time. -It can be discharged by letting a current flow in the opposite direction out of the capacitor.

Capacitor Construction • A capacitor is constructed using a pair of parallel conducting plates +q: positive charge gain due to electrons lost separated by an insulating material Direction of electron displacement (dielectric). • When the two plates of a capacitor are connected to a voltage source as shown, charges are displaced from one side of the capacitor to the other side, thereby establishing an electric field. • The charges continue to be displaced in this manner until the potential difference across the two plates is equal to the potential of voltage source. +q: negative charge gained due to electrons gained

Capacitor Water Pipe Analogy —I • In the water pipe analogy, a capacitor is thought of as a water pipe: – with a rubber diaphragm sealing off each side of the pipe and –a plunger on one end. • When the plunger pushes toward the diaphragm, the water in the pipe forces the diaphragm to stretch until the force of the diaphragm pushing back on the water equals the force on the plunger pipe is charged! • If the plunger is released, the diaphragm will push the plunger back to its original position pipe is discharged. Pipe filled with water Plunger Rubber diaphragm sealing center of pipe

Capacitor Symbols + Fixed capacitor Polarized capacitor Variable capacitor

Inductor Symbols

Ohm’s Law Statement: Current through an ideal conductor is proportional to the applied voltage Conductor is also known as a resistor – An ideal conductor is a material whose resistance does not change with temperature For an ohmic device, Voltage Current Resistance V = Voltage I = Current R = Resistance V I R (Volts = V) (Amperes = A) (Ohms = Ω)

Kirchoff’s Voltage Law • The algebraic sum of voltage around a loop is zero. • Assumption: –Voltage drop across each passive element is in the direction of current flow. I -

Kirchoff’s Current Law • Algebraic sum of all currents entering and leaving a node is zero. • At node A: I 1 A I 2 • Current entering a node is assigned positive sign. Current leaving a node is assigned a negative sign. I 3

Law of Voltage division

Law of Current division

Electrical sources An electrical source is a voltage or current generator capable of supplying energy to a circuit Examples: -AA batteries -12 -Volt car battery -Wall plug

Ideal voltage source An ideal voltage source is a circuit element where the voltage across the source is independent of the current through it. Recall Ohm’s Law: V=IR The internal resistance of an ideal voltage source is zero. If the current through an ideal voltage source is completely determined by the external circuit, it is considered an independent voltage source

Ideal current source An ideal current source is a circuit element where the current through the source is independent of the voltage across it. Recall Ohm’s Law: I = V/R The internal resistance of an ideal current source is infinite. If the voltage across an ideal current source is completely determined by the external circuit, it is considered an independent current source

Dependent Sources A dependent or controlled source depends upon a different voltage or current in the circuit

Different Types of Circuits

Different Types of Circuits current will travel

Series Circuit In a Series Circuit there is only one path for the electric current or electricity to flow.

Series Circuit • All of the loads in a series circuit share the same current. • If there is any break in the circuit, the charges will stop flowing.

Series Circuit Imagine if your refrigerator and a lamp were in a series circuit together. Your refrigerator would run only when the lamp was on. And when the bulb burns out, the refrigerator would stop working.

Series Circuit There are some cases when a series circuit is useful. For example, series circuits are useful in wiring burglar alarms Why? If any part of the circuit in a burglar alarm fails, there will be no current in the system. The lack of current signals that a problem exists, and the alarm will sound. Can you think of any other examples?

Imagine that your house is wired in a series circuit. What would have to happen if you wanted to watch TV? You would have to turn on other appliances in order to watch TV. Stupid right? Circuits in buildings are wired in Parallel.

Parallel Circuit In a Parallel Circuit there is more than one path for the electric current or electricity to flow.

Parallel Circuit • The electric current branches so that electrons flow through each of the paths • If one path is broken, electrons continue to flow to the other paths

Circuit Sort Activity

Comparing Series & Parallel http: //oviattfamily. net/electricity/flash/simple. Circuit. swf

Resistors q Resistance v Property which opposes the flow of current v R = V/I v Unit – Ohms ( ) v Power P = VI = V 2/R = I 2 R q Conductance v Reciprocal of resistance v Symbol: G v Unit – Siemens (S) I + R V -

Example: Resistors in series The resistors in a series circuit are 680 Ω, 1. 5 kΩ, and 2. 2 kΩ. What is the total resistance?

Series circuits A series circuit has only one current path Current through each component is the same In a series circuit, all elements must function for the circuit to be complete

Multiple elements in a series circuit

Example: Voltage sources in series Find the total voltage of the sources shown What happens if you reverse a battery?

Example: Resistors in series The resistors in a series circuit are 680 Ω, 1. 5 kΩ, and 2. 2 kΩ. What is the total resistance? The current through each resistor?

Example: Resistors in parallel The resistors in a parallel circuit are 680 Ω, 1. 5 kΩ, and 2. 2 kΩ. What is the total resistance?

Parallel circuits A parallel circuit has more than one current path branching from the energy source Voltage across each pathway is the same In a parallel circuit, separate current paths function independently of one another

Multiple elements in a parallel circuit For parallel voltage sources, the voltage is the same across all batteries, but the current supplied by each element is a fraction of the total current

Example: Resistors in parallel The resistors in a parallel circuit are 680 Ω, 1. 5 kΩ, and 2. 2 kΩ. What is the total resistance? Voltage across each resistor? Current through each resistor?

Resistive Circuits q. Resistors in series: q. Resistors in parallel: R 1 R 2 R 3

Current Division in Parallel Circuits

Voltage Division in Series Circuits

Star & Delta Connections A A Ra Rc Rab Rca Rb C B C Star Connection Rbc Delta Connection B

Star-Delta Transformation q Delta to Star Transformation: A A Rca C Ra Rab Rc Rbc B C Rb B

Star-Delta Transformation contd… q Star to Delta Transformation: A A Rca C Ra Rab Rc Rbc B C Rb B

Example 1 For the circuit shown, determine the power supplied to the resistive network ( all resistor values are in ’s) Psupplied =47. 06 W

Example 2 Find the potential difference across 10Ω resistor. Also, find the power consumed by it. V 10Ω= 14. 14 V; P 10Ω= 20 W

Summary We started with v. Resistance and its properties Then discussed v. Resistive circuits v. Current Division in Parallel Circuit v. Voltage Division in Series Circuit v. Star-Delta Transformation Concluded with v. Application of star-delta & source transformation concepts.