BASIC ELECTRICAL CIRCUITBASIC ELECTRICAL CIRCUIT

In order to have a complete electrical In order to have a complete electrical circuit three main parts must be circuit three main parts must be present. present.

aa power_source, power_source,

aa load, load, andand

a conductinga conducting pathway.pathway.

A Power SupplyA Power Supply

► A Power Supply is a device that A Power Supply is a device that provides provides potential differencepotential difference so as to so as to force electrons to flow from a negatively force electrons to flow from a negatively charge cell to a positively charged cell. charge cell to a positively charged cell.

►Potential Difference, as discussed in our Potential Difference, as discussed in our earlier chapter is the imbalance in earlier chapter is the imbalance in nature where negative electrons are nature where negative electrons are separated from atoms that are able to separated from atoms that are able to receive atoms.receive atoms.

► Potential Difference can be created by either Potential Difference can be created by either chemical or electromechanical processes. chemical or electromechanical processes.

► The The chemicalchemical process of creating a potential process of creating a potential difference is by inserting differing metals in difference is by inserting differing metals in an acidic solution where the metals interact an acidic solution where the metals interact with the acid to, with one metal, produce with the acid to, with one metal, produce excess electrons and the other metal excess electrons and the other metal produces atoms that are lacking electrons. produces atoms that are lacking electrons. This process is known in the general public This process is known in the general public as a battery. as a battery.

►The The electromechanicalelectromechanical process is to process is to pass wire conductors through pass wire conductors through magnetic fields, this induces electrons magnetic fields, this induces electrons to move through the wire, creating a to move through the wire, creating a current flow.current flow.

► When the battery terminals are When the battery terminals are connected together all of the electrons connected together all of the electrons flow through the wire from the flow through the wire from the negativenegative cell with excess electrons to the cell with excess electrons to the positivepositive cell that contains positive atom cell that contains positive atom that are lacking electrons (these are that are lacking electrons (these are know as holes). know as holes).

►When all electrons have found a partner When all electrons have found a partner hole the battery becomes neutral and, hole the battery becomes neutral and, as we say, is dead (or neutralized). as we say, is dead (or neutralized).

►These terminals are the connection These terminals are the connection points for each cell in the battery. The points for each cell in the battery. The positive cells are marked with a plus positive cells are marked with a plus sign (+) and the negative cells that sign (+) and the negative cells that has too many electrons and is marked has too many electrons and is marked with a negative sign (—). with a negative sign (—).

► These two markings are referred to as These two markings are referred to as polarity polarity markings. markings. All power supplies have polarity but All power supplies have polarity but not all electrical devices have polarity. not all electrical devices have polarity. Whenever polarity is a critical issue, it will be Whenever polarity is a critical issue, it will be marked on the device. marked on the device.

► The technology behind solid-state components The technology behind solid-state components is based on the fact that current can be is based on the fact that current can be directed to flow in a single direction, if current directed to flow in a single direction, if current is allowed to flow in the wrong direction is allowed to flow in the wrong direction components can be damaged. The proper components can be damaged. The proper polarity must be followed to avoid damage to polarity must be followed to avoid damage to equipment and/or people.equipment and/or people.

Throughout the history of electricity / Throughout the history of electricity / electronics there has emerged two electronics there has emerged two theories that describe electricity flow. theories that describe electricity flow. In the early years scientist thought In the early years scientist thought electricity flowed from positive charge electricity flowed from positive charge toward negative charge (similar to toward negative charge (similar to water flowing from a full bucket to an water flowing from a full bucket to an empty one). empty one).

When scientist became aware of atoms When scientist became aware of atoms and the negative charge of an electron and the negative charge of an electron they began to describe current flow as they began to describe current flow as negative to positive. These two negative to positive. These two theories are known as theories are known as conventionalconventional and and electronelectron current flow. It is not of so current flow. It is not of so much importance that you know which much importance that you know which theory is used but which polarity theory is used but which polarity electrical components are connected in.electrical components are connected in.

LoadLoad

►The second aspect a circuit must include The second aspect a circuit must include is a load. A is a load. A loadload is created in a circuit is created in a circuit when the electrical energy produced in a when the electrical energy produced in a circuit is converted to some other form circuit is converted to some other form of energy such as heat, light, or of energy such as heat, light, or magnetism. A light-bulb is a load that magnetism. A light-bulb is a load that produces light. When designing a circuit produces light. When designing a circuit it is important that the power supply it is important that the power supply ratingrating and the load rating should match. and the load rating should match.

► If the lamp is rated at 6 volts, then If the lamp is rated at 6 volts, then the battery should only supply 6 volts the battery should only supply 6 volts of potential difference. If the battery is of potential difference. If the battery is rated at a lower voltage rating, the rated at a lower voltage rating, the lamp will appear dim or will not light. If lamp will appear dim or will not light. If the battery is rated at a much higher the battery is rated at a much higher voltage, the lamp will be damaged by voltage, the lamp will be damaged by the excess electrical energy. the excess electrical energy.

►Often times a resistor can Often times a resistor can simulatesimulate load load in a circuit. No work is done just the in a circuit. No work is done just the decrease in current.decrease in current.

► If a circuit has no resistance the If a circuit has no resistance the electricity will flow too fast and out of electricity will flow too fast and out of control and this will damage control and this will damage components. This situation is know as components. This situation is know as a a shortshort circuit. circuit.

►The two most common ways Resistors The two most common ways Resistors are created either by are created either by carboncarbon material material resistance or by wire resistance or by wire woundwound into coils into coils that by means of electromagnet fields that by means of electromagnet fields resist current flow. When a resistor resist current flow. When a resistor has a high resistance has a high resistance lessless current can current can flow through it which allows the circuit flow through it which allows the circuit builder to control current flow.builder to control current flow.

ConductorsConductors

►The third aspect that must be included to The third aspect that must be included to create a complete circuit is a conductor. create a complete circuit is a conductor. A conductor is a length of material that A conductor is a length of material that will allow electrons to move through it. will allow electrons to move through it. Most often you will work with Most often you will work with coppercopper wire wire as the conductor. The atomic structure of as the conductor. The atomic structure of copper and its availability in nature copper and its availability in nature makes this material an excellent choice makes this material an excellent choice for electrical circuit conductors.for electrical circuit conductors.

►Most conductors are covered in a Most conductors are covered in a plastic coating to provide an plastic coating to provide an insulatinginsulating cover around them. This makes the cover around them. This makes the conductor pathway safe to work with. conductor pathway safe to work with. When components are connected just When components are connected just enough of the isolative cover is enough of the isolative cover is stripped from the ends to connect to stripped from the ends to connect to the components and the rest of the the components and the rest of the wire is protected from a short circuit. wire is protected from a short circuit.

►Although a complete circuit is create Although a complete circuit is create when it includes a power source, a when it includes a power source, a conductor, and a load, almost all conductor, and a load, almost all circuit also include a control device circuit also include a control device know as a know as a switchswitch to start and stop to start and stop current flow. There are many different current flow. There are many different types of switches and we will learn types of switches and we will learn about these later in this lesson. about these later in this lesson.

►To help facilitate the development of To help facilitate the development of electric and electronic circuits a electric and electronic circuits a system of drawings was developed system of drawings was developed known as schematics. A known as schematics. A schematicschematic uses symbols to represent circuit uses symbols to represent circuit components and can show all components and can show all connection in a circuit before you connection in a circuit before you actually solder them together. actually solder them together.

►AA simulator simulator software goes one step software goes one step further by animating schematics to further by animating schematics to work just as real circuits would to show work just as real circuits would to show outcomes without damaging outcomes without damaging components or causing human components or causing human injuries.injuries.

A Simple ExampleA Simple Example

An example of a simple electrical circuit An example of a simple electrical circuit we see quite often is a we see quite often is a flashlightflashlight. It . It consists of a battery (sometimes two consists of a battery (sometimes two or three) as the source of electrical or three) as the source of electrical energy, a small light-bulb as the energy, a small light-bulb as the electrical load, and wires as the electrical load, and wires as the conductors connecting the battery to conductors connecting the battery to the light-bulb. the light-bulb.

In the power supply of this circuit, the In the power supply of this circuit, the battery, which uses chemical reactions, battery, which uses chemical reactions, produce ionization. produce ionization. IonizationIonization is the is the process of producing an excess of process of producing an excess of electrons (negative charge) in one cell electrons (negative charge) in one cell and a depletion of electrons (positive and a depletion of electrons (positive charge) in the other. As the electrons charge) in the other. As the electrons flow through the wire from flow through the wire from -- to to ++ through the light-bulb it changes the through the light-bulb it changes the electron flow into another form; electron flow into another form; lightlight..

►Any electrical circuit that has a power Any electrical circuit that has a power source pushing electrons through a source pushing electrons through a conductive pathway to an electrical conductive pathway to an electrical device that converts electricity flow device that converts electricity flow into other forms of energy can be into other forms of energy can be quantified by three key forces; quantified by three key forces; voltagevoltage, , currentcurrent and and resistanceresistance. .

Power Supplies producePower Supplies produceVoltageVoltage

►Voltage is the unit of measurement Voltage is the unit of measurement that quantifies the potential difference that quantifies the potential difference a power supply produces. What is a power supply produces. What is voltage? voltage? Voltage Voltage is the force behind is the force behind electron flow. Voltage is often supplied electron flow. Voltage is often supplied by chemical reactions in a battery or by chemical reactions in a battery or electro-mechanical actions such as electro-mechanical actions such as generators and turbines.generators and turbines.

►Voltage is measured in units known as Voltage is measured in units known as volts. volts. voltsvolts are abbreviated by are abbreviated by VV is the is the electrical unit used to express the electrical unit used to express the amount of electrical pressure present, amount of electrical pressure present, or the amount of electrical force or the amount of electrical force produced from the present imbalance.produced from the present imbalance.

►The term voltage is used to express the The term voltage is used to express the amount of electrical force in much the amount of electrical force in much the same way we use horsepower to express same way we use horsepower to express the amount of mechanical force for an the amount of mechanical force for an automobile. Electrical pressure or voltage automobile. Electrical pressure or voltage can also be expressed as can also be expressed as potential, potential, potential difference, potential difference, or as or as electromotive electromotive force (emf). force (emf). For our purposes, these For our purposes, these terms mean the same thing. Voltage is terms mean the same thing. Voltage is usually represented by the capital letter usually represented by the capital letter E E or or V.V.

Voltage Pressure causes Voltage Pressure causes Current flowCurrent flow

►The movement of electrons moving The movement of electrons moving through a conductor is known as through a conductor is known as current. The amount of electrons current. The amount of electrons flowing in a conductor is rated in the flowing in a conductor is rated in the electrical unit known as electrical unit known as ampsamps abbreviated as abbreviated as AA. . The ampere is The ampere is represented in mathematical represented in mathematical expressions as the letter expressions as the letter I just as I just as voltage is represented as V. voltage is represented as V.

► A coulomb is a somewhat large quantity of A coulomb is a somewhat large quantity of electrons developed to help count the electrons developed to help count the amount of electrons that flow past a given amount of electrons that flow past a given point in a conductor within a one second point in a conductor within a one second time frame. If 6.24 x 10^18 (one coulomb) time frame. If 6.24 x 10^18 (one coulomb) passes a given point within one a second passes a given point within one a second time frame one Ampere of current is time frame one Ampere of current is flowing. flowing.

► Compare a balloon filled with air to an electrical Compare a balloon filled with air to an electrical battery. The amount of air molecules in the battery. The amount of air molecules in the balloon represents the amount of electrons or balloon represents the amount of electrons or coulombs. The amount of air pressure inside the coulombs. The amount of air pressure inside the balloon is expressed as pounds per square inch balloon is expressed as pounds per square inch (PSI) of air pressure. In the battery, the amount (PSI) of air pressure. In the battery, the amount of electrical pressure inside the battery is of electrical pressure inside the battery is expressed as the voltage rating of the battery. expressed as the voltage rating of the battery. The rate of air flow out of the balloon is similar The rate of air flow out of the balloon is similar to electron flow, or current, from the battery. to electron flow, or current, from the battery.

►The current from the battery in an The current from the battery in an electrical circuit is the volume of the electrical circuit is the volume of the electrons that flow past a given point, electrons that flow past a given point, and is rated in amperes or amps. Just and is rated in amperes or amps. Just as the air will continue to escape from as the air will continue to escape from the balloon until the balloon is empty, the balloon until the balloon is empty, the electron flow can continue as long the electron flow can continue as long as there is voltage or electrical as there is voltage or electrical pressure present in the battery.pressure present in the battery.

ResistanceResistance

► The third aspect that is present in a circuit The third aspect that is present in a circuit that can be measured and quantified is that can be measured and quantified is resistance. resistance. Resistance Resistance is simply the is simply the opposition to the flow of electrons and even in opposition to the flow of electrons and even in the most conductive material there is always the most conductive material there is always some amount of attraction of electrons to some amount of attraction of electrons to protons that would cause resistance to protons that would cause resistance to current flow. Resistance is measured in current flow. Resistance is measured in ohmsohms, , and the electrical symbol for ohm is and the electrical symbol for ohm is (the Greek letter (the Greek letter omegaomega). ).

►The resistance values of elements and The resistance values of elements and compounds differ according to the compounds differ according to the atomic structure of the material. A atomic structure of the material. A good good conductor conductor of electricity is of electricity is anything that permits the free flow of anything that permits the free flow of electrons. electrons.

► A poor conductor of electricity is a material A poor conductor of electricity is a material that will not permit the free flow of that will not permit the free flow of electrons. Extremely poor conductors are electrons. Extremely poor conductors are referred to as referred to as insulators. insulators.

►A A semiconductor semiconductor is a material that is a material that limits the flow of free electrons. A limits the flow of free electrons. A semiconductor is considered neither a semiconductor is considered neither a good conductor nor poor conductor of good conductor nor poor conductor of electricity. Semiconductor materials electricity. Semiconductor materials are at the very heart of modem are at the very heart of modem electronic applications and will be electronic applications and will be explored in depth later in this course. explored in depth later in this course.

►So to explain the basic happenings in a So to explain the basic happenings in a circuit your would say, “When a voltage circuit your would say, “When a voltage across the ends of a resistor across the ends of a resistor currentcurrent begins to flow, and when current is begins to flow, and when current is flowing through a resistor flowing through a resistor heatheat is is dissipated and cause a load in the dissipated and cause a load in the circuit”.circuit”.

End HereEnd Here

Current, AC and DCCurrent, AC and DC

►There are two types of electrical There are two types of electrical current, DC (direct current) and AC current, DC (direct current) and AC (alternating current). The difference (alternating current). The difference between these currents is how they between these currents is how they flow through an electrical circuit. flow through an electrical circuit.

►Direct current Direct current flows in only one direction flows in only one direction through an electrical circuit. In a battery through an electrical circuit. In a battery the chemical reactions cause one cell to the chemical reactions cause one cell to have a surplus of electrons and another have a surplus of electrons and another cell that has a lack of electrons. The cell that has a lack of electrons. The electrons flow in one direction from electrons flow in one direction from negative surplus to positive lack. The negative surplus to positive lack. The battery has a set polarity (positive and battery has a set polarity (positive and negative terminals) and will produce an negative terminals) and will produce an electric current in only one direction. electric current in only one direction.

►Alternating current, Alternating current, as its name as its name implies, flows in both directions. First it implies, flows in both directions. First it flows in one direction, and then it flows in one direction, and then it reverses its flow to the opposite reverses its flow to the opposite direction. direction.

►There are no positive or negative polarity There are no positive or negative polarity markings in alternating current because markings in alternating current because the polarity changes so rapidly in the the polarity changes so rapidly in the typical ac electrical circuit. The terms typical ac electrical circuit. The terms cycle cycle and and hertz hertz are used to describe how are used to describe how fast the current is alternating or changing fast the current is alternating or changing direction in the circuit. A 60 cycle ac direction in the circuit. A 60 cycle ac circuit (operating at 60 hertz) changes circuit (operating at 60 hertz) changes direction 120 times per second. This is direction 120 times per second. This is the standard for ac in the USA.the standard for ac in the USA.

Conventional Current Flow Conventional Current Flow vs. Electron Flow Theoryvs. Electron Flow Theory

►Approximately 200 years ago, scientists Approximately 200 years ago, scientists theorized that electricity had both theorized that electricity had both positive and negative polarities and at positive and negative polarities and at that time they arbitrarily decided that that time they arbitrarily decided that electrical current flowed from positive to electrical current flowed from positive to negative. While it was never actually negative. While it was never actually proven as fact, this theory was accepted proven as fact, this theory was accepted for quite some time. for quite some time. This theory is known This theory is known as the as the conventional current flow theoryconventional current flow theory. .

► As our knowledge of science progressed, As our knowledge of science progressed, and with the discovery of the atom and and with the discovery of the atom and semiconductor electronics, it became semiconductor electronics, it became apparent that the conventional current flow apparent that the conventional current flow theory was incorrect. It is widely accepted theory was incorrect. It is widely accepted that it is the electrons that actually move, that it is the electrons that actually move, and they flow from negative to positive, not and they flow from negative to positive, not from positive to negative. This newer theory from positive to negative. This newer theory is known as is known as electron flow theoryelectron flow theory. .

►The emergence of this new theory The emergence of this new theory caused a controversy that is still in caused a controversy that is still in existence today. For over 150 years all existence today. For over 150 years all circuit designs had been based upon circuit designs had been based upon the old, conventional current flow the old, conventional current flow theory.theory.

►Many circuits and devices still used today are Many circuits and devices still used today are based on the conventional theory. This text based on the conventional theory. This text uses the convention that will make the uses the convention that will make the concepts in each example most easily concepts in each example most easily understood. Most of the figures in this text understood. Most of the figures in this text show electron flow. Regardless of which show electron flow. Regardless of which theory is used to explain the phenomena of theory is used to explain the phenomena of electronics, the most important point is electronics, the most important point is that that the correct polarity must be maintained when the correct polarity must be maintained when building circuits with devices that require a building circuits with devices that require a definite polarity. definite polarity. Examine each example for Examine each example for polarity markings. polarity markings.

Review Questions for Section Review Questions for Section 1.31.3

►1.1. What are the three main parts of What are the three main parts of an electrical circuit?an electrical circuit?

►2.2. The ____________ supplies the The ____________ supplies the electrons that will flow through the electrons that will flow through the circuit.circuit.

►3.3. The __________ provide a path The __________ provide a path through which the electrical energy through which the electrical energy can flow.can flow.

►4.4. The ____________ is where the The ____________ is where the electrical energy is converted to electrical energy is converted to another form of energy.another form of energy.

►5.5. The source has __________ The source has __________ markings that are identified with a ___ markings that are identified with a ___ or ___ symbol.or ___ symbol.

►6.6. The movement of electrons is The movement of electrons is known as ___________________.known as ___________________.

►7.7. Opposition to current flow is calledOpposition to current flow is called►8.8. Opposition to current is measured Opposition to current is measured

in ____________in ____________►9.9. Electrical pressure is measured in Electrical pressure is measured in

________________________

►10.10. ___________ theory states that ___________ theory states that electrons flow from negative to electrons flow from negative to positive.positive.

►11.11. __________ current flows only in one __________ current flows only in one direction while __________ current direction while __________ current constantly changes direction.constantly changes direction.

►12.12. Connecting the correct ___________ Connecting the correct ___________ of an electrical device in an electrical of an electrical device in an electrical circuit is more important than which circuit is more important than which theory of current flow is used.theory of current flow is used.

►13.13. A(n) __________ circuit provides A(n) __________ circuit provides only one path for electron flow.only one path for electron flow.

►14.14. A(n) __________ circuit provides A(n) __________ circuit provides more than one path for electron flow.more than one path for electron flow.

If Electricity isn’t Static If Electricity isn’t Static it is Dynamic.it is Dynamic.

►Once a pathway connects a place of Once a pathway connects a place of electrical excess to an electrical place of electrical excess to an electrical place of lacking. Entropy kicks in and the lacking. Entropy kicks in and the electronics start to flow (potential energy electronics start to flow (potential energy has changed to kinetic). This movement of has changed to kinetic). This movement of electrons is most commonly referred to as electrons is most commonly referred to as CURRENT flow. Due to normal thermal CURRENT flow. Due to normal thermal agitation (heat), some electrons in the agitation (heat), some electrons in the outer orbit of an atom will break away and outer orbit of an atom will break away and become free. become free.

►They remain free for only a fraction of They remain free for only a fraction of a second, yet at any given time there a second, yet at any given time there are millions, indeed trillions of FREE are millions, indeed trillions of FREE ELECTRONSELECTRONS1212 in a particular in a particular substance. If we can get these free substance. If we can get these free electrons to move in one direction we electrons to move in one direction we have what is known as electronic have what is known as electronic CURRENT FLOW.CURRENT FLOW.

►Some materials have many more free Some materials have many more free electrons than others. Rubber, for electrons than others. Rubber, for example, has almost none at any example, has almost none at any temperature, while copper is just loaded temperature, while copper is just loaded with them. Rubber is considered a good with them. Rubber is considered a good InsulatorInsulator1313. This means that it will resist . This means that it will resist current flow because it has so few free current flow because it has so few free electrons that can move. Yet copper is an electrons that can move. Yet copper is an excellent conductor because it has many excellent conductor because it has many free electrons ready to move.free electrons ready to move.

►To get free electrons to move in one To get free electrons to move in one direction (current flow), an outside direction (current flow), an outside force of some type is needed. This force of some type is needed. This outside force is known as VOLTAGE. outside force is known as VOLTAGE. As it has been said, at any given time As it has been said, at any given time there are trillions of free electrons in a there are trillions of free electrons in a particular material such copper. particular material such copper. (Actually any metal will have countless (Actually any metal will have countless free electrons.) free electrons.)

►However, these free electrons are However, these free electrons are "dancing around" in all directions and "dancing around" in all directions and do not constitute current flow. A do not constitute current flow. A voltage force lines up these free voltage force lines up these free electrons and pushes them all in the electrons and pushes them all in the same direction.same direction.

► If the voltage force where too strong it would If the voltage force where too strong it would not only move free electrons but also begin to not only move free electrons but also begin to force stable electrons from the atoms they are force stable electrons from the atoms they are attached to and break down the materials attached to and break down the materials integrity. This is what happens when a wire is integrity. This is what happens when a wire is burned apart when too current is sent through burned apart when too current is sent through it. In order to have the right amount of force it. In order to have the right amount of force applied to a material to produce electron flow applied to a material to produce electron flow the force has to be strong enough to overcome the force has to be strong enough to overcome the opposition of movement that exists due to the opposition of movement that exists due to the attraction of electron and its nucleus. the attraction of electron and its nucleus.

►The opposition to current flow due to this The opposition to current flow due to this attraction is known as RESISTANCE. The attraction is known as RESISTANCE. The right amount of voltage must be enough right amount of voltage must be enough to overcome an electrons resistance yet to overcome an electrons resistance yet not enough to force too many electron to not enough to force too many electron to move causing material deterioration. If move causing material deterioration. If the resistance to electron flow is stronger the resistance to electron flow is stronger than the voltage pressure then current than the voltage pressure then current does not flow but a build up of electrons does not flow but a build up of electrons continues; this is known as STATIC continues; this is known as STATIC electricity. electricity.

►The term static mean stationary and is The term static mean stationary and is an example of potential energy applied an example of potential energy applied to electricity. If the voltage continues to to electricity. If the voltage continues to cause pressure, it will increase in cause pressure, it will increase in strength until it produces enough force strength until it produces enough force to overcome the resistance barrier and to overcome the resistance barrier and then it will break through causing now then it will break through causing now Kinetic energy or aka current flow. This Kinetic energy or aka current flow. This phenomenon is exhibited in nature when phenomenon is exhibited in nature when lighting strikes the earth during a storm.lighting strikes the earth during a storm.

summarysummary

► If all three of the characteristics If all three of the characteristics discussed above are present a closed discussed above are present a closed electrical system is created known as electrical system is created known as an electrical circuit. The block diagram an electrical circuit. The block diagram of a simple circuit shown below in fig 1-of a simple circuit shown below in fig 1-1 shows a closed circuit that has a 1 shows a closed circuit that has a source of voltage - the battery, current source of voltage - the battery, current flowing through the conductors, and flowing through the conductors, and resistance in the wires and light bulb. resistance in the wires and light bulb.

► It, along with more complex circuits It, along with more complex circuits contains the "big three" in electronics: contains the "big three" in electronics: Current - Voltage - Resistance. If the Current - Voltage - Resistance. If the circuit is ever broken or any on of the circuit is ever broken or any on of the “big three” are missing the circuit is “big three” are missing the circuit is said to be opensaid to be open1616..