Unit 1 Atomic Structure Objectives:

Unit 1 Atomic Structure Objectives:
List the three major parts of an atom. State the law of charges. Discuss the law of centripetal force. Discuss the differences between semiconductors and insulators.

Unit 1 Atomic Structure History
The Greeks were the first to discover electricity 2500 years ago. The Greeks called amber elektron. About 300 years ago Charles DuFay studied the force of repulsion and attraction using a glass rod.

List of charged materials.
Unit 1 Atomic Structure List of charged materials.

Unlike charges attract and like charges repel.
Unit 1 Atomic Structure Unlike charges attract and like charges repel.

Unit 1 Atomic Structure Atoms
The atom is the basic building block of the universe. An element is a substance that cannot be chemically divided into a simpler substance. The principal parts of an atom are the electron, neutron, and proton.

Unit 1 Atomic Structure Atomic Theory
An element is composed of only one type of atom. The atomic number of an element is the same as the number of protons in the nucleus. The Periodic Table of Elements lists all the types of atoms or elements known to mankind. A molecule is the result of the joining of two or more different types of atoms.

Water can exist in three states.
Unit 1 Atomic Structure Water can exist in three states.

Unit 1 Atomic Structure Table of elements.

Unit 1 Atomic Structure The three principal parts of an atom are the electron, the neutron, and the proton.

Unit 1 Atomic Structure The electron has a negative charge and orbits the nucleus. The proton has a positive charge. The neutron has no charge and combines with the proton to form the nucleus.

Unit 1 Atomic Structure Protons have a positive charge.
Electrons have a negative charge.

Opposite charges attract!
Unit 1 Atomic Structure The Law of Charges Opposite charges attract!

Unit 1 Atomic Structure The Law of Charges Like charges repel.

Unit 1 Atomic Structure Centripetal Force prevents an object from pulling away from its axis point.

Unit 1 Atomic Structure Electrons form orbits or shells that surround the nucleus.

Electrons orbit the nucleus in a circular fashion.
Unit 1 Atomic Structure Electrons orbit the nucleus in a circular fashion.

Unit 1 Atomic Structure Valence electrons are located in the outer orbit of an atom.

A copper atom contains 29 electrons and has one valence electron.
Unit 1 Atomic Structure A copper atom contains 29 electrons and has one valence electron.

Unit 1 Atomic Structure Electron Flow
Electricity is the flow of electrons. This happens when a free electron knocks another electron free out of its orbit. The striking electron settles into a new orbit. This process repeated many times creates electrical flow.

Unit 1 Atomic Structure An electron of one atom knocks an electron of another atom out of orbit and takes its place.

The energy of the cue ball is transferred to the ball being struck.
Unit 1 Atomic Structure The energy of the cue ball is transferred to the ball being struck.

The energy of the striking electron is divided.
Unit 1 Atomic Structure The energy of the striking electron is divided.

The energy of the cue ball is divided between the other two balls.
Unit 1 Atomic Structure The energy of the cue ball is divided between the other two balls.

Unit 1 Atomic Structure The energy of the striking electron is divided among the eight electrons.

Unit 1 Atomic Structure Semiconductors
Semiconductors are materials that are neither good conductors nor good insulators. They contain four valence electrons. When heated, their resistance decreases. Two common materials are silicon and germanium.

Semiconductors contain four valence electrons.
Unit 1 Atomic Structure Semiconductors contain four valence electrons.

Unit 1 Atomic Structure Molecules are formed when atoms are joined together.

Unit 1 Atomic Structure There are six basic methods for producing electricity: 1. magnetism 2. chemical action 3. pressure 4. heat 5. friction 6. light

Unit 1 Atomic Structure There are five basic effects electricity can cause: 1. magnetism 2. chemical reactions 3. pressure 4. heat 5. light

Producing sound with electricity.
Unit 1 Atomic Structure Producing sound with electricity.

Unit 1 Atomic Structure Insulators
Insulators resist the flow of electricity. They contain seven or eight valence electrons. Examples of insulators are: rubber, plastic, glass, and wood.

Unit 1 Atomic Structure Review:
The atom is the smallest part of an element. The three basic parts of an atom are the proton, electron, and neutron. Protons have a positive charge, electrons a negative charge, and neutrons no charge.

Valence electrons are located in the outer orbit of an atom. Insulators are materials that do not provide an easy path for electron flow. Insulators are made from materials containing seven or eight valence electrons.

Semiconductors contain four valence electrons. Molecules are formed by joining atoms together. Semiconductors are materials that are neither good conductors nor good insulators.

Six basic methods for producing electricity are magnetism, chemical action, light, heat, pressure, and friction. Five basic effects that can be caused by electricity are magnetism, chemical reactions, light, heat ,and pressure.

The law of charges states that like charges repel and opposite charges attract.

Unit 2 Electrical Quantities and Ohm’s Law
Objectives: Define a coulomb. Define an ampere. Define a volt. Define an ohm. Define a watt.

Objectives: Compute electrical values using Ohm’s law. Discuss basic types of circuits. Use the Ohm’s wheel charts.

A coulomb is a quantity measurement for electrons. One coulomb contains 6.25 x 1018 electrons, or 6,250,000,000,000,000,000 electrons.

The ampere is a measurement of the amount of electricity that is flowing through a circuit. One ampere (A) is defined as one coulomb of electricity flowing past a given point in one second.

Compare and contrast these two systems.

There are two theories about current flow. Electron flow theory describes current flow from negative to positive. Conventional current flow theory states electrical current flows from positive to negative.

Conventional current flow theory and electron flow theory.

Electrons moving from atom to atom.

Electrical sources are divided into two basic types: Direct Current (DC) which is unidirectional (one way).     Alternating Current (AC) which is bidirectional (two way, or back and forth).    

A complete path must exist before electricity can flow through a circuit. A circuit with a complete path for electrical flow is called a closed circuit. If the circuit path is incomplete or broken, this is called an open circuit.

A simple switch closes and opens an electrical circuit.

A short circuit has an unintended shorter pathway.

The basic principle of the instantaneous effect of electric impulses.

The impulse of electricity can travel faster than light. It would take light 1.3 seconds to travel around the earth 10 times. If a wire were wrapped around the earth 10 times, when the switch was closed the light would come on almost instantly.

A volt or voltage is electrical pressure.

An ohm is the unit of resistance or opposition to the flow of electricity.

The watt is the unit of electrical power.

Force equals flow rate times pressure.

Amperes times volts equals watts.

Common power units.

Ohm’s law states that in a DC (Direct Current) circuit, the current is directly proportional to the voltage and inversely proportional to the resistance. E(volts) = I(amps) x R(ohms)

Ohm’s Law Symbols: P is the symbol for Watts. E is the symbol for Volts. I is the symbol for Amperes. R is the symbol for Resistance or Ohms.

Ohm’s Law states that it takes one volt to push one ampere through one ohm. E = Volts E = I x R R = Resistance I = Amps

Using the Ohm’s law chart. E = I x R I = E / R R = E / I

Adding P (watts) to the Ohm’s law chart. P = E2 / R P = E x I P = I2 x R I = I = P / E I = E / R R = E / I R = P / I2 R = E2 / P E = E = I x R E = P / I

Remember: E = EMF, or voltage I = intensity of current, or amperage R = resistance in ohms P = power in watts E(volts) = I(amperes) x R(ohms) P(watts) = I(amperes) x E(volts)

Metric Units

Review: A coulomb is a quantity measurement of electrons. An ampere (A) is one coulomb per second. Either the letter I, which stands for intensity of current flow, or the letter A, which stands for amperes, can be used in Ohm’s law formulas.

Review: Voltage is referred to as electric pressure, potential difference, or electromotive force. An E or a V can be used to represent voltage in Ohm’s law formulas. An ohm (Ω) is a measurement of resistance (R) in an electric circuit.

Review: The watt (W) is a measurement of power in an electrical circuit. It is represented by either a W or a P (power) in Ohm’s law formulas. Electric measurements are generally expressed in engineering notation.

Review: Engineering notation differs from the standard metric system in that it uses steps of 1000 instead of steps of 10. Before current can flow, there must be a complete circuit. A short circuit has little or no resistance.

Unit 3 Static Electricity
Objectives: Discuss the nature of static electricity. Use an electroscope to determine unknown charges. Discuss lightning protection. List nuisance charges of static electricity. List useful charges of static electricity.

Static charges can cause a painful shock!

Charges Static charges can be a nuisance, or dangerous, or beneficial. Electric shocks from walking on carpet can be annoying. Electrostatic discharge can ruin sensitive electronic components. Copy machines and sandpaper rely on the application of static electricity.

Grains of sand receive a charge to help them stand apart when making sandpaper.

Charges Electronic air filters called precipitators use static charges to attract small particles in the air and trap them in the filter. The word static means not moving. Electrostatic charges build up on insulators. A static charge can be positive or negative.

Electronic air cleaner or precipitator

Producing a static charge.

Electroscope The electroscope was an early device that indicated the polarity of a charged object. The electroscope uses a metal ball to transfer a known polarity charge to thin metal leaves. When an object with an unknown charge is brought near the metal ball, the action of the leaves reveals the nature of the object’s charge.

Electroscope.

Charging the electroscope with a negative static charge.

The action of the leaves reveals the polarity of the pen’s charge.

Lightning The best example of static electricity in nature is lightning. The movement of water droplets in a thundercloud generates a static charge. Lightning occurs when the positive and negative areas have the potential difference to overcome the air’s resistance.

The typical thundercloud contains areas both positively and negatively charged.

Lightning Protection Lightning rods are used to help protect objects from lightning. Lightning rods provide a safe path to channel the electric discharge. A lightning arrestor is also used for protection.

Lightning travels from negative to positive areas.

A lightning rod provides an easy path to ground.

Useful static charges are often used in spray painting.

The drum of a copy machine is coated with selenium.

The drum receives a positive charge.

The image is transferred to the selenium drum.

Negatively charged powder is applied to the positively charged drum.

The negatively charged powder is attracted to the positively charged paper.

Review: The word static means not moving. An object is positively charged by removing electrons. An object is negatively charged by adding electrons. An electroscope is a device used to determine the polarity of an object.

Review: Static charges accumulate on insulator materials. Lightning is an example of a natural static charge.

Unit 6 Series Circuits Objectives:
Discuss the properties of series circuits. List three rules for solving electrical values of series circuits. Compute values of voltage, current, resistance, and power for series circuits. Compute the values of voltage drop in a series circuit using the voltage divider formula.

Unit 6 Series Circuits A series circuit has only one path for current flow.

Unit 6 Series Circuits Fuses and circuit breakers are connected in series. All the circuit current must flow through the fuse. When the fuse opens, the circuit is disconnected from the power source. Fuse Generator

Unit 6 Series Circuits In a series circuit, the sum of all the voltage drops across all the resistors must equal the source voltage.

Unit 6 Series Circuits The series circuit shows four resistors having different voltage drops. Again, the sum of the voltage drops equals the applied source voltage in a series circuit.

Rules for Calculating Series Circuit Values
Unit 6 Series Circuits Rules for Calculating Series Circuit Values The current is the same at any point in the circuit. The total resistance is the sum of the individual resistors. The applied voltage is equal to the sum of the voltage drops across all the resistors.

Unit 6 Series Circuits Formulas for Calculating Series Circuit Values:
ITOTAL = I1 = I2 = I3 ……= INUMBER OF RESISTORS RTOTAL = R1 + R2 + R3 ..…+ RNUMBER OF RESISTORS ETOTAL = E1 + E2 + E3 …..+ ENUMBER OF RESISTORS

Example of Series Circuit Values
Unit 6 Series Circuits Example of Series Circuit Values ITOTAL = I1 = I2 = I3 = 2 A RTOTAL = 20 Ω + 10 Ω + 30 Ω = 60 Ω ETOTAL = 40 V + 20 V + 60 V = 120 V Please insert figure 6-6

Unit 6 Series Circuits Power in a Series Circuit
The total power used in a circuit is equal to the sum of the power used by all parts. PTOTAL = P1 + P2 + P3 …… PNUMBER OF RESISTORS Please insert Figure 6-21

Unit 6 Series Circuits The voltage divider circuits are used to provide different voltages between specific points.

Unit 6 Series Circuits Review:
Series circuits have only one path for current flow. The individual voltage drops in a series circuit can be added to equal the applied voltage. The current is the same at any point in a series circuit.

The individual resistors can be added to equal the total resistance of the circuit. Fuses and circuit breakers are connected in series with the devices they are intended to protect.

The total power in any circuit is equal to the sum of the power dissipated by all parts of the circuit. When the source voltage and total resistance are known, the voltage drop across each element can be computed using the general voltage divider formula.

Unit 7 Parallel Circuits
Objectives: Discuss the characteristics of parallel circuits. State the three rules for solving electrical values of resistance for parallel circuits. Solve the missing values in a parallel circuit using the three rules and Ohm’s law.

Objectives: Calculate current values using the current divider formula.

Three Parallel Circuit Rules The voltage drop across any branch is equal to the source voltage. The total current is equal to the sum of the branch currents. The total resistance is the reciprocal of the sum of the reciprocals of each individual branch.

Parallel circuits are circuits that have more than one path for current to flow. I (total current) = 3A + 2A + 1A = 6A

Lights and receptacles are connected in parallel. Each light or receptacle needs 120 volts. Panel

The voltage drop across any branch of a parallel circuit is the same as the applied (source) voltage. Panel

The voltage drop across any branch of a parallel circuit is the same as the source voltage. E = 120 V E3 = 120 V E1 = 120 V E2 = 120 V

Parallel Resistance Formulas The Reciprocal Formula: 1/R(total) = 1/R1 + 1/R2 + 1/R3 …1/R(number) The Resistors of Equal Value Formula: R(total) = R(any resistor)/N(number of resistors) The Product-Over-Sum Formula: R(total) = (R1 x R2) / (R1 + R2)

The Reciprocal Formula The total resistance of a parallel circuit is the reciprocal of the sum of the reciprocals of the individual branches. 1/R(total) = 1/R1 + 1/R2 + 1/R3 …1/R(number) R(total) R1 R2 R3

Reciprocal Formula Example 1/R(total) = 1/R1 + 1/R2 + 1/R3 …1/R(number) 1/R(total) = 1/50 = 1/ / /100 R(total) = 50 ohms R(total)50 Ω R1 150 Ω R2 300 Ω R3 100 Ω

Resistors of Equal Value Formula The total resistance of a parallel circuit is equal to the value of one resistor, divided by the number of resistors. R(total) = R(any resistor) / N(number of resistors) R(total) R1 R2 R3

Resistors of Equal Value Example R(total) = R(any resistor)/N(number of resistors) R(total) = 24(any resistor)/3(number of resistors) R(total) = 24/3 = 8 ohms R(total) 8 Ω R1 24 Ω R2 24 Ω R3 24 Ω

The Product-Over-Sum Formula The total resistance of two resistors or branches is equal to the value of the product of the resistors divided by the sum of resistors. R(total) = (R1 x R2) / (R1 + R2) R(total) R1 R2 R3

Product Over Sum Formula Example Step One: R(2 & 3) = (R2 x R3) / (R2 + R3) R(2 & 3) = (30 x 60) / ( ) = 1800 / 90 R(2 & 3) = 20 ohms R(total) 10 Ω R1 20 Ω R2 30 Ω R3 60 Ω

Product-Over-Sum Formula Example Step Two: R(1 & 2 & 3) = R1 x R(2 & 3) / R1 + R(2 & 3) R(1 & 2 & 3) = (20 x 20) / ( ) = 400 / 40 = 10 R(1 & 2 & 3) = 10 ohms = R(total) R(total) 10 Ω R1 20 Ω R2 30 Ω R3 60 Ω

Product-Over-Sum Formula Review The ohm value of two branches is combined. This process is repeated using the combined ohm value with the next branch. When all the branches are combined, this equals the total resistance.

Current Divider Formula I(unknown) = I(total) x R(total)/R(unknown) E = 120 V I = 24 A R = 5 Ω P = 2880 W E3 = 120 V I3 = 4 A R3 = 30 Ω P3 = 360 W E1 = 120 V I1 = 8 A R1 = 15 Ω P1 = 960 W E2 = 120 V I2 = 12 A R2 = 10 Ω P2 = 120 W

Current Divider Formula Example I(unknown) = I(total) x R(total)/R(unknown) Find I1, I2, and I3. E = 160 V I = 2 A R = 80 Ω P = 320 W E3 = 160 V I3 = ? A R3 = 120 Ω P3 = 360 W E1 = 160 V I1 = ? A R1 = 1200 Ω P1 = 960 W E2 = 160 V I2 = ? A R2 = 300 Ω P2 = 120 W

Current Divider Formula Example I(unknown) = I(total) x R(total)/R(unknown) I1 = 2 x (80/1200) = .133 amps E = 160 V I = 2 A R = 80 Ω P = 320 W E3 = 160 V I3 = ? A R3 = 120 Ω P3 = 360 W E1 = 160 V I1 = .133 A R1 = 1200 Ω P1 = 960 W E2 = 160 V I2 = ? A R2 = 300 Ω P2 = 120 W

Current Divider Formula Example I(unknown) = I(total) x R(total)/R(unknown) I2 = 2 x (80/300) = .533 amps E = 160 V I = 2 A R = 80 Ω P = 320 W E3 = 160 V I3 = ? A R3 = 120 Ω P3 = 360 W E1 = 160 V I1 = .133 A R1 = 1200 Ω P1 = 960 W E2 = 160 V I2 = .533 A R2 = 300 Ω P2 = 120 W

Current Divider Formula Example I(unknown) = I(total) x R(total)/R(unknown) I3 = 2 x (80/120) = 1.33 amps E = 160 V I = 2 A R = 80 Ω P = 320 W E3 = 160 V I3 = 1.33 A R3 = 120 Ω P3 = 360 W E1 = 160 V I1 = .133 A R1 = 1200 Ω P1 = 960 W E2 = 160 V I2 = .5 A R2 = 300 Ω P2 = 120 W

Review: Parallel circuits have more than one circuit path or branch. The total current is equal to the sum of the branch currents. The voltage drop across any branch is equal to the source voltage. The total resistance is less than any branch resistance.

Review: The total resistance can be found using the reciprocal formula. The product-over-sum formula and the resistors of equal value formula are special formulas. Circuits in homes are connected in parallel.

Review: The total power is equal to the sum of the resistors’ power. Parallel circuits are current dividers. The amount of current flow through each branch of a parallel circuit is inversely proportional to its resistance.

Unit 8 Combination Circuits
Objectives: Define a combination circuit. List the rules for parallel circuits. List the rules for series circuits. Solve for combination circuit values.

Characteristics There are multiple current paths. Resistors may be in series or parallel with other resistors. A node is where three or more paths come together. The total power is the sum of the resistors’ power.

A simple combination circuit.

Solving Combination Circuits E1 = ? V I1 = ? A R1 = 325 Ω E3 = ? V I3 = ? A R3 = 150 Ω E = ? V I = 1 A R = ? Ω E2 = ? V I2 = ? A R2 = 275 Ω E4 = ? V I4 = ? A R4 = 250 Ω

Series Circuit Rules The current is the same at any point in the circuit. The total resistance is the sum of the individual resistances. The sum of the voltage drops or the individual resistors must equal the applied (source) voltage.

Parallel Circuit Rules The voltage across any circuit branch is the same as the applied (source) voltage. The total current is the sum of the current through all of the circuit branches. The total resistance is equal to the reciprocal of the sum of the reciprocals of the branch resistances.

Simplifying the Circuit Resistors in series can be combined to form an equivalent resistance. Resistors in parallel can be combined to form an equivalent resistance. The equivalent resistances are used to draw simplified equivalent circuits.

Reducing Combination Circuits Combine R1 & R2, and R3 & R4. R1 = 325 Ω R3 = 150 Ω R = ? Ω R2 = 275 Ω R4 = 250 Ω

Reducing Combination Circuits Redraw simplified circuit. R1 + R2 = R1&2 = 600 ohms R3 + R4 = R3&4 = 400 ohms R = ? Ω R1&2 = 600 Ω R3&4 = 400 Ω

Solving Combination Circuits Solve for the applied voltage using Ohm’s law. Note that the I(total) was given data. E(source) = I(total) x R(total) = 1 x 240 = 240 V E = 240 V I = 1 A R = 240 Ω R1&2 = 600 Ω R3&4 = 400 Ω

Solving Combination Circuits Solve for the branch currents using Ohm’s law. E(source) = E1&2 = E3&4 I1&2 = E1&2 / R1&2 = 240/600 = 0.4 A E = 240 V I = 1 A R = 240 Ω E = 240 V I = 0.4 A R1&2 = 600 Ω R3&4 = 400 Ω

Solving Combination Circuits Solve for the branch currents using Ohm’s law. E(source) = E1&2 = E3&4 I3&4 = E3&4 / R3&4 = 240/400 = 0.6 A E = 240 V I = 1 A R = 240 Ω E1&2 = 240 V I = 0.4 A R1&2 = 600 Ω E3&4 = 240 V I = 0.6 A R3&4 = 400 Ω

Solving Combination Circuits Expand the circuit back to the original circuit. Branch currents remain the same. E1 = ? V I1 = 0.4 A R1 = 240 Ω E3 = ? V I3 = 0.6 A R3 = 240 Ω E = 240 V I = 1 A R = 240 Ω E2 = ? V I2 = 0.4 A R2 = 240 Ω E4 = ? V I4 = 0.6 A R4 = 240 Ω

Solving Combination Circuits Solve for each voltage drop using Ohm’s law. E1 = I1 x R1 = 0.4 x 325 = 130 V E1 = 130 V I1 = 0.4 A R1 = 325 Ω E3 = ? V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = ? V I2 = 0.4 A R2 = 275 Ω E4 = ? V I4 = 0.6 A R4 = 250 Ω

Solving Combination Circuits Solve for each voltage drop using Ohm’s law. E2 = I2 x R2 = 0.4 x 275 = 110 V E1 = 130 V I1 = 0.4 A R1 = 325 Ω E3 = ? V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = 110 V I2 = 0.4 A R2 = 275 Ω E4 = ? V I4 = 0.6 A R4 = 250 Ω

Solving Combination Circuits Solve for each voltage drop using Ohm’s law. E3 = I3 x R3 = 0.6 x 150 = 90 V E1 = 130 V I1 = 0.4 A R1 = 325 Ω E3 = 90 V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = 110 V I2 = 0.4 A R2 = 275 Ω E4 = ? V I4 = 0.6 A R4 = 250 Ω

Solving Combination Circuits Solve for each voltage drop using Ohm’s law. E4 = I4 x R4 = 0.6 x 250 = 150 V E1 = 130 V I1 = 0.4 A R1 = 325 Ω E3 = 90 V I 3= 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = 110 V I2 = 0.4 A R2 = 275 Ω E4= 150 V I4 = 0.6 A R4 = 250 Ω

Kirchhoff’s Laws The algebraic sum of the voltage sources and voltage drops in a closed circuit must equal zero. This law states that the sum of the voltage drops in a series circuit must equal the applied voltage. The algebraic sum of the current entering and leaving a point must equal zero. The second law is for parallel circuits and states that the total current is the sum of all the branch currents.

Solving Combination Circuits Review E1 = ? V I1 = ? A R1 = 325 Ω E3 = ? V I3 = ? A R3 = 150 Ω E = ? V I = 1 A R = ? Ω E2 = ? V I2 = ? A R2 = 275 Ω E4 = ? V I4 = ? A R4 = 250 Ω

Solving Combination Circuits Review: Combine R1 & R2, and R3 & R4 R1 = 325 Ω R3 = 150 Ω R = ? Ω R2 = 275 Ω R4 = 250 Ω

Solving Combination Circuits Review: Redraw simplified circuit. R1 + R2 = R1&2 = 600 ohms R3 + R4 = R3&4 = 400 ohms R = ? Ω R1&2 = 600 Ω R3&4 = 400 Ω

Solving Combination Circuits Review: Solve for the applied voltage using Ohm’s Law. Note that the I(total) was given data. E(source) = I(total) x R(total) = 1 x 240 = 240 V E = 240 V I = 1 A R = 240 Ω R1&2 = 600 Ω R3&4 = 400 Ω

Solving Combination Circuits Review: Solve for the branch currents using Ohm’s law. E(source) = E1&2 = E3&4 I1&2 = E1&2 / R1&2 = 240/600 = 0.4 A E = 240 V I = 1 A R = 240 Ω E = 240 V I = 0.4 A R1&2 = 600 Ω R3&4 = 400 Ω

Solving Combination Circuits Review: Solve for the branch currents using Ohm’s law. E(source) = E1&2 = E3&4 I3&4 = E3&4 / R3&4 = 240/400 = 0.6 A E = 240 V I = 1 A R = 240 Ω E1&2 = 240 V I = 0.4 A R1&2 = 600 Ω E3&4 = 240 V I = 0.6 A R3&4 = 400 Ω

Solving Combination Circuits Review: Expand the circuit back to the original circuit. Branch currents remain the same. E1 = ? V I1 = 0.4 A R1 = 240 Ω E3 = ? V I3 = 0.6 A R3 = 240 Ω E = 240 V I = 1 A R = 240 Ω E2 = ? V I2 = 0.4 A R2 = 240 Ω E4 = ? V I4 = 0.6 A R4 = 240 Ω

Solving Combination Circuits Review: Solve for each voltage drop using Ohm’s law. E1 = I1 x R1 = 0.4 x 325 = 130 V E1 = 130 V I1= 0.4 A R1 = 325 Ω E3 = ? V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = ? V I2 = 0.4 A R2 = 275 Ω E4 = ? V I4 = 0.6 A R4 = 250 Ω

Solving Combination Circuits Review: Solve for each voltage drop using Ohm’s law. E2 = I2 x R2 = 0.4 x 275 = 110 V E1 = 130 V I1 = 0.4 A R1 = 325 Ω E3 = ? V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = 110 V I2 = 0.4 A R2 = 275 Ω E4 = ? V I4 = 0.6 A R4 = 250 Ω

Solving Combination Circuits Review: Solve for each voltage drop using Ohm’s law. E3 = I3 x R3 = 0.6 x 150 = 90 V E1 = 130 V I1= 0.4 A R1 = 325 Ω E3 = 90 V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = 110 V I2 = 0.4 A R2 = 275 Ω E4 = ? V I4 = 0.6 A R4 = 250 Ω

Solving Combination Circuits Review: Solve for each voltage drop using Ohm’s law. E4 = I4 x R4 = 0.6 x 250 = 150 V E1 = 130 V I1= 0.4 A R1 = 325 Ω E3 = 90 V I3 = 0.6 A R3 = 150 Ω E = 240 V I = 1 A R = 240 Ω E2 = 110 V I2 = 0.4 A R2 = 275 Ω E4 = 150 V I4 = 0.6 A R4 = 250 Ω

Review: The three rules for series circuits are: The current is the same at any point in the circuit. The total resistance is the sum of the individual resistances. The applied voltage is equal to the sum of the voltage drops across the individual components.

Review: The three rules for parallel circuits are: The total voltage is the same as the voltage across any branch. The total current is the sum of the individual currents. The total resistance is the reciprocal of the sum of the reciprocals of the branch resistances.

Review: Combination circuits are circuits that contain both series and parallel branches. A node is where three or more paths come together. The total power is the sum of all the circuit resistors’ power.

Review: When solving combination circuits, simplify, reduce, and redraw equivalent value circuits. Apply the series rules and the parallel rules selectively to various parts of the combination circuit.

Unit 9 Measuring Instruments
Objectives: Discuss the operation of a d’Arsonval meter movement. Connect a voltmeter to a circuit. Read an analog multimeter. Connect an ammeter. Measure resistance using an ohmmeter.

Analog meters are characterized by the fact that they use a pointer and scale to indicate their value. One of the common types of meters uses the d’Arsonval type of meter movement. Analog meters use a moving coil placed between the poles of a magnet.

Basic d’Arsonval meter movement.

Basic d’Arsonval meter movement with rectifier to change AC voltage to DC voltage.

The voltmeter is designed to be connected directly across the source of power.

Reading an analog meter is similar to reading a speedometer or fuel gauge.

The ammeter is used to measure current and must be connected in series with the load to permit the load to limit the current flow.

A shunt is used to set the value of the ammeter.

Many electricians use the clamp-on type of AC ammeter. Please note the clamp-on ammeter reads only one conductor at a time.

Ohmmeters The ohmmeter is used to measure resistance. There are two basic types: analog or digital. The common VOM (volt-ohm-milliammeter) contains an ohmmeter. An ohmmeter should always be readjusted to zero when the scale is changed.

Digital Ohmmeters Digital ohmmeters display the resistance in figures instead of using a meter movement. They operate by measuring the voltage drop across a resistor. The ohmmeter, whether digital or analog, must never be connected to a circuit when the power is turned on!

Digital Ohmmeter

Digital Voltmeter

Low-impedance Voltage Tester The low-impedance voltage tester has a very large current draw compared to other types of voltmeters and should never be used to test low-power circuits.

Low-impedance Voltage Tester This tester has an impedance of 5000 Ω and can generally be used to measure voltages as high as 600 V.

Low-impedance Voltage Tester This is also known as a solenoid type tester. This tester is not susceptible to giving the misleading voltage readings caused by high-impedance ground paths or feedback voltages.

Low-impedance Voltage Tester High-impedance ground paths can produce misleading voltage readings.

Low-impedance Voltage Tester

Reading a Digital Meter Many digital meters are auto-ranging, which means that they select the range scale automatically. This type will display a notation beside the numerical digits to indicate the meter scale.

Review: The d’Arsonval movement is one of the common types of meters. The d’Arsonval movement operates only on DC currents or rectified AC current. Voltmeters have a high resistance and are designed to be connected directly across the power line.

Review: Ammeters have a low resistance and must be connected in series with a load. Shunts are used to change the value of DC ammeters. Clamp-on ammeters read only one conductor at a time.

Review: 7. Ohmmeters are used to measure the resistance in a circuit. 8. There are two basic types of Ohmmeters: analog and digital. 9. Ohmmeters must never be connected to a circuit that has power applied to it.

Review: 10. Digital multimeters display their value in digits instead of using a meter movement. 11. Digital ohmmeters measure resistance by measuring the voltage drop across an unknown resistor when a known amount of current flows through it.

Review: 12. Low-impedance voltage testers (solenoid type) are not susceptible to indicating a negligible voltage caused by a high-impedance ground or feedback.

Unit 15 Alternating Current
Objectives: Discuss differences between direct and alternating current. Be able to compute instantaneous values of voltage and current for a sine wave. Be able to compute peak, RMS, and average values of voltage and current. Discuss the phase relationship or voltage and current in a pure resistive circuit.

The single greatest advantage of alternating current is that AC current can be transformed and DC current cannot be transformed. This allows high-voltage electrical power to be distributed with smaller wires and lower amperage. The electrical power is then transformed to a lower voltage where it is needed.

Alternating current flows first in one direction and then in the other direction.

A graph view of a square wave.

A square wave alternating current produced by a switch and two batteries.

The sine wave is the most common of all the AC wave forms.

The sine wave is produced by rotating machines.

One sine wave is 360 electrical degrees.

The voltage at any point along the sine wave is equal to the maximum, or peak, value times the sine of the angle of rotation.

As the loop approaches 90° of rotation, the flux lines are cut at a faster rate.

E(INST) = E(MAX) x SINE θ E(INST) = the voltage at any point on the wave form E(MAX) = the maximum, or peak, voltage SINE θ = the sine of angle theta, the angle of rotation

Instantaneous values of voltage along a sine wave.

Peak, Peak-to-Peak, and RMS values along a sine wave.

RMS = Peak x 0.707 Peak = RMS x 1.414

In a pure resistive circuit, the voltage and current are in phase.

Review: Most of the electrical power generated in the world is alternating current. Alternating current can be transformed and direct current cannot. Alternating current reverses its direction of flow at periodic intervals.

Review: The most common AC wave form is the sine wave. There are 360 degrees in one complete sine wave. Sine waves are produced by rotating machines.

Review: The instantaneous voltage at any point on a sine wave is equal to the peak, or maximum, voltage times the sine of the angle of rotation. The peak-to-peak voltage is the amount of voltage attained by the wave form. The peak value is the maximum amount of voltage attained by the wave form.

Review: The current and voltage in a pure resistive circuit are in phase with each other.

Unit 16 Inductance in AC Circuits
Objectives: Discuss the properties of inductance in an alternating current circuit. Discuss inductive reactance. Compute values of inductive reactance and inductance. Discuss the relationship of voltage and current in a pure inductive circuit.

Objectives: Be able to compute values for inductors connected in series or parallel. Discuss reactive power (VARs).

A continually changing magnetic field induces a voltage into any conductor.

As current flow increases through a coil, a magnetic field is created around the coil.

As current flow decreases through a coil, the magnetic field collapses.

The applied voltage and induced voltage are 180° out of phase.

Inductive reactance is the current-limiting property of an inductor. The inductive reactance symbol is XL . The unit of measurement is in ohms, just like resistance, and Ohm’s law formulas can be used.

Inductive Reactance XL = 2πfL XL = inductive reactance 2 = a constant π = F = frequency in hertz (Hz) L = inductance in henrys (H)

Coils with turns close together produce more inductance than coils with turns far apart.

Three factors that determine induced voltage: 1. The number of turns of wire. 2. The strength of the magnetic field. 3. The speed of the cutting action.

Circuit current is limited by inductive reactance. XL = 2πfL = 377 x .8 = Ω I = E / XL = 120 V / Ω = A

Inductors connected in series. LT = L1 + L2 + L3 XLT = XL1 + XL2 + XL3

Inductors connected in parallel. 1/LT = 1/L1 + 1/L2 + 1/L3 1/XLT = 1/XL /XL2 + 1/XL3

Applied Voltage Current Flow In a pure inductive circuit, the current lags the applied voltage by 90°.

Reactive Power VARs = EL x IL VARs = EL2 / XL VARs = IL2 x XL EL = voltage applied to an inductor IL = current flow through an inductor XL = inductive reactance

Review: Induced voltage is proportional to the rate of change of current. Induced voltage is always opposite in polarity to the applied voltage. Inductive reactance is a countervoltage that limits the flow of current, as does resistance.

Review: Inductive reactance is measured in ohms. Inductive reactance is proportional to the inductance of the coil and the frequency of the line. Inductive reactance is symbolized by XL. Inductance is measured in henrys (H) and is symbolized by the letter L.

Review: When inductors are connected in series, the total inductance is equal to the sum of all the inductors. When inductors are connected in parallel, the reciprocal of the total inductance is equal to the sum of the reciprocals of all the inductors.

Review: The current lags the applied voltage by 90° in a pure inductive circuit. Reactive power is measured in VARs.

Unit 27 Single-Phase Transformers
Objectives: Discuss the different types of transformers. List transformer symbols and formulas. Discuss polarity markings.

A transformer is a magnetically operated machine. All values of a transformer are proportional to its turns ratio.

The primary winding is connected to the incoming power supply. The secondary winding is connected to the driven load.

This is an isolation transformer. The secondary winding is physically and electrically isolated from the primary winding.

The two windings of an isolation transformer are linked together by the magnetic field.

The isolation transformer greatly reduces voltage spikes.

Basic construction of an isolation transformer.

Each set of windings (primary and secondary) is formed from loops of wire wrapped around the core. Each loop of wire is called a turn. The ratio of the primary and secondary voltages is determined by the ratio of the number of turns in the primary and secondary windings. The volts-per-turn ratio is the same on both the primary and secondary windings.

Transformer Symbols NP = number of turns in the primary NS = number of turns in the secondary EP = voltage of the primary ES = voltage of the secondary IP = current in the primary IS = current in the secondary

Transformer Formulas EP / ES = NP / NS EP x NS = ES x NP EP x IP = ES x IS NP x IP = NS x IS

The distribution transformer is a common type of isolation transformer. This transformer changes the high voltage from the power company to the common 240/120 V.

The control transformer is another common type of isolation transformer. This transformer reduces high voltage to the value needed by control circuits.

Polarity dots are placed on transformer schematics to indicate points that have the same polarity at the same time.

Review: All values of voltage, current, and impedance in a transformer are proportional to the turns ratio. The primary winding of a transformer is connected to the source voltage. The secondary winding is connected to the load.

Review: An isolation transformer has its primary and secondary voltage electrically and mechanically separated. Isolation transformers help filter voltage and current spikes. Polarity dots are often added to schematic diagrams to indicate transformer polarity.

Unit 1 Atomic Structure Objectives:

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