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BENE 1113 PRINCIPLES OF ELECTRICAL AND ELECTRONICS CHAPTER 1 “INTRODUCTION ELECTRICITY” OF 1 The meaning of the subject title • Principles – a comprehensive and fundamental • • law, a rule of conduct Electrical – is a field of engineering that deals with the study and application of electricity, electronics and electromagnetism Electronics - is the study of the flow of charge through various materials and devices such as semiconductors, resistors, inductors, capacitors, nano-structures and vacuum tubes. 2 Electrical versus Electronic • Electrical engineering may or may not encompass electronic engineering. Where a distinction is made, electrical engineering is considered to deal with the problems associated with large-scale electrical systems such as power transmission and motor control, whereas electronic engineering deals with the study of small-scale electronic systems including computers and integrated circuits 3 Learning outcome of this topic • At the end of the topic, the students should be able to explain the basic concept of electrical and electronics. 4 TOPICS COVERED: • • • • • • • • • Introduction of electricity Static and dynamic electricity Electric current and electric charge Electrical base units Electric field Electric flux Electrostatic Coulomb’s law Ampere’s law 5 1.1 INTRODUCTION OF ELECTRICITY The importance study of electricity: • It is hard to imagine the world without electricity, it touches and influences our daily lives in hundreds of ways. • Without electricity, most of the things we use and enjoy today would not be possible. • Study of electricity will be based upon the electron theory, which assumes that all electrical and electronic effects are due to the movement of electrons from place to place. • Electricity is the flow of electrons through simple materials and devices. 6 1.1.1 Review of Electricity • Molecule: the combination of the two or more atoms. • Atom: the smallest particle into which an element can de divided. • Nucleus: the positively charged central part of atom. • Neutron: the neutral particles in the nucleus that behave a combination of proton and electron. • Proton: the positively charged particles in the nucleus. 7 • Electron: the very small negatively charged particles which are circle the nucleus in orbits. • Free electrons: electrons that have left their orbit in an atom and are wandering freely through a material. • Electric current: the movement of free electrons. • Positive charge: A deficiency of electrons. • Negative charge: A surplus of electrons. 8 1.2 STATIC AND DYNAMIC ELECTRICITY • You walk across the carpet, reach for the door knob and..........ZAP!!! You get a shock. • Or, pull off your hat and......BOING!!! All your hair stands on end. What is going on here? 9 Answer: Static Electricity • If you walk across a carpet, electrons move from the rug to you. Now you have extra electrons. Touch a door knob and ZAP! The electrons move from you to the knob. You get a shock. • When you pull your hat off, it rubs against your hair. Electrons move from your hair to the hat. Now each of the hairs has the same positive charge. the hairs try to move away from each other. The furthest they can get is to stand up and away from all the other hairs. 10 • Static electricity is the situation where electrical charges build up on the surface of a material. • It is called “static” because there is no current flowing as in AC or DC electricity. • Static electricity is usually caused when materials are rubbed together. The result is that objects may be attracted to each other or may even cause a spark to jump from one object to the other. • Common examples of static electricity in action of flyaway hair and the sparks that can occur when you touch something. 11 Dynamic Electricity • When two bodies are at different potentials, an electric force exists between them. • This force can cause an electron flow between the bodies if a conducting path exist between them. • The electric force is termed an electromotive force (e.m.f), it is measured by the potential difference in Volts between two points. • If points of different potential are joined by an electrical conductor, the electrons will be forced from the point where there is a surplus of electrons to a point where there is a deficiency. 12 • Electrons will flow from a point of higher electron potential to one of lower electron potential whenever a conducting path exists between those points. • The rate of flow of electricity is governed by the two factors; potential difference and electrical material. 13 Unit of Charge • The charge on an electron is so small that it is not convenient to select it as the unit of charge. • In practice, Coulomb is used as the unit of charge. • 1 C of charge is equal to the charge on 6.25x1018 electrons. 1 Coulomb=charge on 6.25x1018 electrons/protons -Q : 6.25x1018 (more electron than proton) +Q : 6.25x1018 (more proton than electron) Charge proton, e: 1.602 x 10 -19 C Charge electron, -e: 1.602 x 10 -19 C 14 – Total charge; number of electrons Q 18 6.25 10 electrons/C • Exercises: 1. How many Coulombs of charge do 93.8 x 1016 electron represent? 2. How many electrons does it take to have 3C of charge? 15 1.3 ELECTRIC CURRENT AND ELECTRIC CHARGE • All atoms are bound together by forces of attraction between nucleus and its electrons. • Electrons in the outer orbits of an atom, however are attracted to their nucleus less powerfully that are electrons whose orbits are nearer the nucleus. • In certain material( electrical conductor), these outer electrons are so weakly bound to their nucleus that they can easily be forced away from it altogether and left to other atoms at random. • Such electrons are called free electrons. It is directional movement of free electrons which makes an electric current. 16 • Electrons which have been forced out of their orbits create a deficiency of electrons in the atoms they leave and will cause a surplus of electrons at the point where they come to rest. • A material with a deficiency of electrons is positively charged; one possessing a surplus of electrons is negatively charged. • When these charges exist and not in motion, it is called a static electricity. 17 • Static electricity usually involves nonconductors. But if the materials were conductors, then the free electrons easily flow back toward the positive charges and the material would be neutral or uncharged. • Like charge (both positive or both negative) will repeal each other while unlike charge (1 positive and 1 negative) will attract each other. 18 1.4 ELECTRICAL BASE UNITS 1. Coulomb – The unit of charge is Coulomb (C), where 1C is 1 Ampere second. – The Coulomb can be defined as the quantity of electricity which flows past a given in an electric circuit when a current of 1 Ampere is maintained for 1 second. – Thus, Q=It where Q: magnitude of charge I: current t: time 19 – Exercises: • What is the current if 2 C passes a point in 5 s? • Then coulombs of charge flow past a given point in a wire in 2 s. What is the current in amperes? • The charge flowing through a wire is 0.16 C every 64 ms. Determine the current in amperes. • Determine how long it will take 4 x 1016 electrons to pass through wire if the current is 5 mA. Answers 0.4 A 5A 2.50A 1.28s 2. Electrical potential and e.m.f (Voltage) – The unit of electric potential and e.m.f are volt(V), where 1 volt is 1 joule per coulomb. – 1 volt can be defined as the difference in potential between two points in a conductor which, when carrying a current of 1 ampere, dissipates a power of 1 watt. Q= I t – Thus, watt joule / sec ond ampere ampere joule coulomb Volt 21 – Exercises: a) If 50J of energy are available for every 10 C of charge, what is the voltage? b) Find the voltage between two points if 60J of energy are required to move a charge of 20 C between the two points. c) Determine the energy expended when moving a charge of 50 µC between two points if the voltage between the points is 6V. Answers a) 5V b) 3V c) 300µJ 3. Resistance – The unit of resistance is ohm where 1 ohm is 1 volt per ampere. – It can be defined as the resistance between two points in a conductor when a constant electric potential of 1 volt applied at the points produces a current flow of 1 ampere in the conductor. – Thus, R= V/I where; V: potential difference across two points I: current flowing between the two points 23 – the schematic symbol is shown below – Conductance is the reciprocal of resistance. – The unit is in Siemens (S) 1 G R Resistor Colour Codes Color Resistance value, first three bands: First band- 1st digit Second band- 2nd digit *Third band- multiplier (number of zeros following the 2nd digit) Fourth band- tolerance Digit Multiplier Tolerance Black 0 10 0 Brown 1 10 1 1% (five band) Red 2 10 2 2% (five band) Orange 3 10 3 Yellow 4 10 4 Green 5 10 5 Blue 6 10 6 Violet 7 10 7 Gray 8 10 8 White 9 10 9 Gold ±5% 10 -1 5% (four band) Silver ± 10% 10 -2 10% (four band) No band ± 20% * For resistance values less than 10W, the third band is either gold or silver. Gold is for a multiplier of 0.1 and silver is for a multiplier of 0.01. • What is the resistance and the tolerance? Alphanumeric Labeling • Two or three digits, and one of the letters R, K, or M are used to identify a resistance value. • The letter is used to indicate the multiplier, and its position is used to indicate decimal point position. Power • When current is forced through a resistance, work is said have been done. Power is the rate of working, represented by "P". Energy is the capacity to do work. • Power is energy per time or the rate of working, represented by "P". The standard unit used in electricity is the Watt (W) = 1 Joule / second. • The amount of power consumed by an electrical device is the rate at which it dissipates energy. 2 V P IV I R R 2 1.5 ELECTRIC FIELD • Like charge will repeal each other while unlike charge will attract each other. • There is a field of force that surrounds the charges and the effect of attraction or repulsion is due to the field. • This field or force is called an electric field of force. It is also sometimes called an electrostatic field or a dielectric field since it can exist in air, glass, paper, vacuum or in any other dielectric or insulating material. • The space or field in which a charge experiences a force is called an electric field or electrostatic field. 29 Electric field lines have the following properties: • They start on a positive charge and end on a negative charge. • They never cross. • They are closer together in regions where the field is stronger and further apart where the field is weak. 30 1.6 ELECTRIC FLUX • The total electric lines of force which flow outward from a positive charge is called electric flux. • Electric flux is a measure of the overall size of electric field and it is measured in Coulomb, C. • The symbol for electric flux is psi,Ψ. • The electric flux density at any section in an electric field is the electric flux crossing normally per unit area of that section: Electric flux density , D C / m2 A where, : electric flux in Coulomb A : area in m 2 • Electric flux density is a vector quantity: possessing both magnitude and direction. 31 1.7 ELECTROSTATIC • Another situation where charges do not move but remain static or stationary on the bodies, such a situation will arise when the charged bodies are separated by some insulating medium, disallowing the movement of electrons. • This is called static electricity and the branch of engineering which deals with static electricity is called electrostatics. • The most useful outcomes of static electricity are the development of lightning rod and the capacitor. 32 1.8 COULOMB’S LAW • First law: related to the nature of force between two charged bodies. “like charges repel each other while unlike charges attract each other” • Second law: tell about the magnitude of force between two charged bodies. “The force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.” 33 Mathematically; where; F: force in Newtons Qa, Qb: charge in Coulomb r: distance in meter k: constant( the value depends upon medium in which the charges are placed and the system of units employed) k is given by; where; ε0 : absolute permittivity of vacuum or air εr: relative permittivity of the medium in which the charges are placed ε0: 8.85x10-12 F/m εr: the value is different for different media (for vacuum or air= 1) 34 Example: Two small conducting spheres A and B having charges of -2.5 x 106 C and -2.5 x 10-6 C respectively are allowed to touch one another briefly. After touching, they separate until the force between them is 0.2 N. What is the distance between two charges? (Coulomb's constant, k: 9.0 x 109 N.m2.C-2.) Solution: r = 53 cm 35 1.9 ELECTRIC POTENTIAL • When a body is charged, work is done by charging it. The work done is stored in the body in the form of potential energy. • The charged body has the capacity to do work by moving other charge either by attraction or repulsion. • The ability or capacity of the charged body to do work is called electric potential. • The greater the capacity of a charged body to do work, the greater is its electric potential. Electric potential,V work done ch arg e 36 • The work done is measured in joule and charge in Coulomb, therefore the unit of electric potential will be joule/coulomb or Volt. • A body is said to have an electric potential of 1 Volt if 1 joule of work is done to give it a charge of 1 Coulomb. • We can say that a body has an electric potential of 5Volt, it means that 5 joule of work has been done to charge the body to 1 Coulomb. 37 Exercises • Determine the voltage • 10J / 1C • 5J / 2C • 100J / 25C • If 50J of energy are available for every 10C of charge, what is the voltage? • 500J of energy are used to move 100C of charge through a resistor. What is the voltage across the resistor? 1.10 POTENTIAL DIFFERENCE • If two bodies have different electric potentials, a potential difference exist between the bodies. • The difference in the potentials of two charged bodies is called potential difference. A +5V B +3V (i) A B (ii) 39 1.9.1 CONCEPT of e.m.f and POTENTIAL DIFFERENCE • The e.m.f of a device (battery), is a measure of the energy the battery gives to each coulomb of charge. • Thus, if a battery supplies 4 joules of energy per coulomb, we say that it has an e.m.f of 4 Volts. • The potential difference between two points, say A and B, is the measure of energy used by 1 coulomb charge in moving from A to B. • Thus, if potential difference between A and B is 2 Volts, it means that each coulomb will give energy of 2 joule in moving from A to B. 40 1.10 AMPERE’S LAW Ampere’s Law states that: “for any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop” B l o I where; B : magnetic flux density l : length of conductor o : permeabili ty I : current 41 Basic Circuit Measurement • Multimeter Digital Multimeters (DMM) Analog Multimeter • Meter symbols Measuring Current • Most analog ammeters have a number of possible settings for the maximum possible current that can be measured; for example: 2 A, 200 mA, 20 mA, 2 mA. You should always start by turning the setting to the highest possible rating (for example, 2 A). If the ammeter reading is too small from the selected scale, then you can reduce the scale to get the reading. It is important not to overshoot the maximum value that can be read. • For example, if the current is about 75 mA, then the ammeter would be set to the 200 mA scale for the most accurate reading. Setting to the 20 mA scale would overload the ammeter and most likely open its internal fuse. Measuring Voltage Measuring Resistance Measured Numbers • Error : The difference between the true value and the measured value • Accuracy : The degree to which a measured value represents the true or accepted value of a quantity. A measurement is said to be accurate if the error is small. • Precision : The repeatability or consistency of a measurement • Resolution – The smallest increment of quantity that the meter can measure. The smaller the increment, the better the resolution. 0.01V 0.001V Chapter 1: Introduction to Electricity 49 Passive Components • Passive components: Components that do not supply voltage or current Color bands Resistance material (carbon composition) Insulation coating Leads – Examples • • • • Resistors Capacitors Inductor Transformer Foil Mica Foil Mica Foil Mica Foil Mica capacitor_ Tantalum electrolytic capacitor (polarized) 50 Active Components • The components that have their own power source. • Passive components are used in conjunction with active components to form an electronic system – Voltage and current sources • Battery, Generator, Fuel cell • Transistor • Integrated Circuit (IC) THANK YOU 52