Basics Of Electricity-Introduction
Basics of ElectricityA quickSTEP Online Course Siemens industry, Inc.www.usa.siemens.com/step
TrademarksSiemens is a trademark of Siemens AG. Product names mentioned may be trademarks or registeredtrademarks of their respective companies.Other trademarks are the property of their respective owners. Siemens Industry, Inc. 2016Page 2
Course TopicsWelcome to Basics of Electricity. This coursecovers the following topics:IntroductionChapter 1 – Direct Current Direct Current Basics DC Circuits MagnetismChapter 2 – Alternating Current Alternating Current Basics Inductance and Capacitance AC Circuits TransformersFinal ExamIf you do not have a basic understanding ofelectricity, complete this course before startingother quickSTEP online courses. Siemens Industry, Inc. 2016Page 3
Course ObjectivesUpon completion of this course you will be able to Explain the difference between conductors and insulatorsUse Ohm’s Law to calculate current, voltage, and resistanceCalculate equivalent resistance for series, parallel, or series-parallel circuitsCalculate voltage drop across a resistorCalculate power given other basic valuesIdentify factors that determine the strength and polarity of a current-carryingcoil’s magnetic fieldDetermine peak, instantaneous, and effective values of an AC sine waveDefine inductive reactance, capacitive reactance, and impedanceCalculate total impedance of a simple AC circuitExplain the difference between real power and apparent power in an AC circuitDetermine how a transformer turns ratio affects secondary voltage and current Siemens Industry, Inc. 2016Page 4
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Chapter 1 – Direct CurrentThis chapter covers the followingtopics: Direct Current Basics DC Circuits Magnetism Siemens Industry, Inc. 2016Page 1-1
AtomsAll matter is composed atoms. Atoms have a nucleus withelectrons moving around it. The nucleus is composed ofprotons and neutrons (not shown).In their neutral state, atoms have an equal number ofelectrons and protons. Electrons have a negative charge.Protons have a positive charge . Neutrons are neutral. Thenegative charge of the electrons is balanced by the positivecharge of the protons. Electrons are bound in their orbit bytheir attraction to protons. Siemens Industry, Inc. 2016Page 1-2
Free ElectronsElectrons in the outer band can become free of their orbitby the application of some external force such asmovement through a magnetic field, friction, or chemicalaction. These are referred to as free electrons.A free electron leaves a void which can be filled by anelectron forced out of orbit from another atom. As freeelectrons move from one atom to the next an electron flowis produced. This is the basis of electricity. Siemens Industry, Inc. 2016Page 1-3
ConductorsAn electric current is produced when free electrons movefrom one atom to the next. Materials that permit manyelectrons to move freely are called conductors.Copper, gold, silver, and aluminum are examples ofmaterials that are good conductors. Copper is widely usedas a conductor because it is one of the best conductors andis relatively inexpensive. Siemens Industry, Inc. 2016Page 1-4
InsulatorsMaterials that allow few free electrons are called insulators.Materials such as plastic, rubber, glass, mica, and ceramicare examples of materials that are good insulators.An electrical cable is one example of how conductors andinsulators are used together. Electrons flow along a copperconductor in a circuit and the insulator around the outside ofthe copper conductor keeps electrons in the conductor. Siemens Industry, Inc. 2016Page 1-5
SemiconductorsSemiconductor materials, such as silicon, can be used tomanufacture devices that have characteristics of bothconductors and insulators.Many semiconductor devices act like a conductor when anexternal force is applied in one direction and like aninsulator when an external force is applied in the oppositedirection.This principle is basic to the operation of transistors, diodes,and other solid-state electronic devices. Siemens Industry, Inc. 2016Page 1-6
Electric ChargesElements are defined by the number of electrons in orbitaround the nucleus of an atom and by the number ofprotons in the nucleus. A hydrogen atom, for example, hasonly one electron and one proton. An aluminum atom has13 electrons and 13 protons. An atom with an equal numberof electrons and protons is said to be electrically neutral.Electrons in the outer band of an atom are easily displacedby the application of some external force. Electrons whichare forced out of their orbits can result in a lack of electronswhere they leave and an excess of electrons where theycome to rest.A material with more protons than electrons has a netpositive charge, and a material with more electrons thanprotons has a net negative charge. A positive or negativecharge is caused by an absence or excess of electrons,because the number of protons in an atom remainsconstant. Siemens Industry, Inc. 2016Page 1-7
Attraction and Repulsion of Electric ChargesThe old saying, “opposites attract,” is true when dealingwith electric charges. Charged bodies have an invisibleelectric field around them. When two unlike-charged bodiesare brought together, their electric fields attract one body tothe other. When two like-charged bodies are broughttogether, their electric fields repel one body from the other.During the 18th century a French scientist, Charles A.Coulomb, studied fields of force that surround chargedbodies. Coulomb discovered that charged bodies attract orrepel each other with a force that is directly proportional tothe product of the charges and inversely proportional to thesquare of the distance between them.Today we call this Coulomb’s Law of Charges. Simply put,the force of attraction or repulsion depends on the strengthof the charges and the distance between them. Siemens Industry, Inc. 2016Page 1-8
CurrentElectricity is the flow of electrons in a conductor from oneatom to the next atom in the same general direction. Thisflow of electrons is referred to as current and is designatedby the symbol “I”.Current is measured in amperes, which is often shortenedto “amps”. The letter “A” is the symbol for amps. Becausethe amount of voltage present can vary significantly, metricunit prefixes are sometimes used. For example, a current of0.001 amps is equal to 1 milliamp or 1 mA for short.Current that constantly flows in the same direction is calleddirect current (DC). Current that periodically changesdirection is called alternating current (AC). Siemens Industry, Inc. 2016Page 1-9
Direction of Current FlowSome authorities distinguish between electron flow andcurrent flow.Conventional current flow theory ignores the flow ofelectrons and states that current flows from positive tonegative.Electric circuits can be correctly analyzed using eitherconventional current flow or electron flow; however, to avoidconfusion, this course uses the electron flow concept whichstates that electrons flow from negative to positive. Siemens Industry, Inc. 2016Page 1-10
VoltageThe force that causes current to flow through a conductor iscalled a difference in potential, electromotive force (emf), orvoltage. Voltage is designated by the letter “E” or the letter“V.” The unit of measurement for voltage is volts which isalso designated by the letter “V.” Because the amount ofvoltage present can vary significantly, metric unit prefixesare sometimes used. For example, a voltage of 1000 voltsis equal to 1 kilovolt or 1kV for short.A voltage can be generated in various ways. A battery usesan electrochemical process. A car’s alternator and a powerplant generator utilize a magnetic induction process.All voltage sources share the characteristic of an excess ofelectrons at one terminal and a shortage at the otherterminal. This results in a difference of potential betweenthe two terminals.For a DC voltage source, the polarity of the terminals doesnot change, so the resulting current constantly flows in thesame direction. Siemens Industry, Inc. 2016The terminals of an AC voltage source periodically changepolarity, causing the current flow direction to change witheach switch in polarity.Page 1-11
ResistanceA third factor that plays a role in an electrical circuit isresistance. Resistance is the property of a circuit,component, or material that opposes current flow. Allmaterial resists the flow of electrical current to some extent.The amount of resistance depends upon the composition,length, cross-section, and temperature of the resistivematerial. For any specific material at a constanttemperature, the resistance of a conductor increases withan increase of length or a decrease in cross-section.Resistance is designated by the symbol “R.” The unit ofmeasurement for resistance is the ohm, symbolized by theGreek letter omega ( . Because 1 ohm is a small unit andcircuit resistances are often large values, metric unitprefixes are often used. For example, 1 million ohms isequal to 1 Megaohm or 1 M for short.While all circuit components have resistance, a resistor is acomponent manufactured to provide a designatedresistance that is often shown in color coded bands aroundthe resistor. Siemens Industry, Inc. 2016Page 1-12
Ohm’s LawA simple electric circuit consists of a voltage source, sometype of load, and conductors to allow electrons to flowbetween the voltage source and the load.Ohm’s law defines the relationship between current,voltage, and resistance and shows that current variesdirectly with voltage and inversely with resistance. Siemens Industry, Inc. 2016Page 1-13
Ohm’s Law TriangleOhm’s law can be expressed in three ways. There is aneasy way to remember which form of Ohm’s law to use.First, draw a triangle with the letters for current, voltage andresistance positioned as shown in the accompanyingillustration.Then, when you need to use the ohms law formula, pointyour finger on the value you want to calculate. Theremaining letters make up the formula. Siemens Industry, Inc. 2016Page 1-14
Ohm’s Law ExampleThe accompanying illustration shows that if you know anytwo Ohm’s law values, you can easily find the third valueusing the appropriate Ohm’s law formula. Siemens Industry, Inc. 2016Page 1-15
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Chapter 1 – Direct CurrentThis chapter covers the followingtopics: Direct Current Basics DC Circuits Magnetism Siemens Industry, Inc. 2016Page 1-17
Series Circuit ResistanceA series circuit is formed when any number of resistors areconnected end-to-end so that there is only one path forcurrent to flow. The resistors can be actual resistors orother devices that have resistance.The accompanying illustration shows five resistorsconnected end-to-end. There is one path of current flowfrom the negative terminal of the voltage source through allfive resistors and returning to the positive terminal.The total resistance in a series circuit is determined byadding all the resistor values. Although the unit forresistance is the ohm, different metric unit prefixes, such askilo (k) or mega (M) are often used. Therefore, it isimportant to convert all resistance values to the same unitsbefore adding. Siemens Industry, Inc. 2016Page 1-18
Series Circuit Voltage and CurrentThe current in a series circuit can be determined usingOhm’s law. First, total the resistance, and then divide thesource voltage by the total resistance.This current flows through each resistor in the circuit. Thevoltage measured across each resistor can be calculatedusing Ohm’s law. The voltage across a resistor is oftenreferred to as a voltage drop. The sum of the voltage dropsacross each resistor is equal to the source voltage.The accompanying illustration shows two voltmeters, onemeasuring total voltage, and one measuring the voltageacross R3. Siemens Industry, Inc. 2016Page 1-19
Parallel CircuitsA parallel circuit is formed when two or more resistancesare placed in a circuit side-by-side so that current can flowthrough more than one path.The accompanying illustration shows the simplest parallelcircuit, two parallel resistors. There are two paths of currentflow. One path is from the negative terminal of the batterythrough R1 returning to the positive terminal. The secondpath is from the negative terminal of the battery through R2returning to the positive terminal of the battery.The current through any resistor can be determined bydividing the circuit voltage by the resistance of that resistor.The total current is the sum of the branch currents. Siemens Industry, Inc. 2016Page 1-20
Parallel Circuit ResistanceThe total resistance for a parallel circuit with any number ofresistors can be calculated using the formula shown in theaccompanying illustration.In the unique example where all resistors have the sameresistance, the total resistance is equal to the resistance ofone resistor divided by the number of resistors. Siemens Industry, Inc. 2016Page 1-21
Parallel Circuit Resistance ExampleThe accompanying illustration shows a circuit with threeparallel resistors. See if you can complete the totalresistance calculation. Then go to the next page of thiscourse to see the solution. Siemens Industry, Inc. 2016Page 1-22
Parallel Circuit Resistance SolutionNote the total resistance calculation for this circuit. Siemens Industry, Inc. 2016Page 1-23
Parallel Circuit Current ExampleCurrent in each of the branches of a parallel circuit can becalculated by dividing the circuit voltage, which is the samefor all branches, by the resistance of the branch.The total circuit current can be calculated by adding thecurrent for all branches or by dividing the circuit voltage bythe total resistance.See if you can complete the calculations for each branchcurrent and for the total current. Then go to the next pageof this course to see the solution. Siemens Industry, Inc. 2016Page 1-24
Parallel Circuit Current ExampleNote the current calculations for this circuit. Siemens Industry, Inc. 2016Page 1-25
Series-Parallel CircuitsSeries-parallel circuits are also known as compoundcircuits. At least three resistors are required to form aseries-parallel circuit. The accompanying illustration showsthe two simplest series-parallel circuits.The circuit on the left has two parallel resistors in serieswith another resistor. The circuit on the right has two seriesresistors in parallel with another resistor.Series-parallel circuits are usually more complex than thecircuits shown here, but by using the circuit formulasdiscussed earlier in this course, you can easily determinecircuit characteristics. Siemens Industry, Inc. 2016Page 1-26
Series-Parallel Circuit Resistance CalculationsThe accompanying illustration shows how total resistancecan be determined for two series-parallel circuits in twoeasy steps for each circuit.More complex circuits require more steps, but each step isrelatively simple. In addition, by using Ohm’s law, you canalso solve for current and voltage throughout each circuit, ifthe source voltage is known. Siemens Industry, Inc. 2016Page 1-27
Series-Parallel Circuit Current CalculationsUsing the same two series-parallel circuits as in theprevious example, but with source voltages included, theaccompanying illustration shows how Ohm’s law can beused to calculate current values. Siemens Industry, Inc. 2016Page 1-28
Power in a DC CircuitWhenever a force of any kind causes motion, work isaccomplished. If a force is exerted without causing motion,then no work is done.In an electrical circuit, voltage applied to a conductor causeselectrons to flow. Voltage is the force and electron flow is themotion. The rate at which work is done is called power and isrepresented by the symbol “P.”Power is measured in watts, represented by the symbol “W.”In a direct current circuit, one watt is the rate at which work isdone when 1 volt causes a current of 1 amp.As shown on the left, from the formula power (P) current (I)times voltage (E), the other formulas for power can bederived using Ohm’s law. Siemens Industry, Inc. 2016Page 1-29
DC Circuit Power ExampleThe accompanying illustration shows how power can becalculated using any of the power formulas. Siemens Industry, Inc. 2016Page 1-30
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Chapter 1 – Direct CurrentThis chapter covers the followingtopics: Direct Current Basics DC Circuits Magnetism Siemens Industry, Inc. 2016Page 1-32
Permanent MagnetsMagnetism and electricity are related concepts. Magnetismcan be used to produce electric current and electric currentproduces a magnetic field.When we think of a permanent magnet, we often envision ahorseshoe or bar magnet or a compass needle, butpermanent magnets come in many shapes.However, all magnets have two characteristics. They attractiron and, if free to move (like the compass needle), amagnet will assume a north-south orientation. Siemens Industry, Inc. 2016Page 1-33
Magnetic Lines of FluxEvery magnet has two poles, a north pole and a south pole.Invisible magnetic lines of flux leave the north pole andenter the south pole.Although the lines of flux are invisible, the effects ofmagnetic fields can be made visible. When a sheet of paperis placed on a magnet and iron filings loosely scattered overit, the filings arrange themselves along the
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