PSAA CurriculumPSAA CurriculumUnitUnit

Physical Science SystemsPhysical Science Systems

Problem AreaProblem AreaEnergy and Power SystemsEnergy and Power Systems

Resistance in Series and Resistance in Series and Parallel CircuitsParallel Circuits

LessonLesson

Christmas Lights…Christmas Lights…Series or Parallel Circuits?Series or Parallel Circuits?

Before plugging in the lights, which string Before plugging in the lights, which string is connected in series and which one is is connected in series and which one is connected in parallel?connected in parallel?

Now that the lights are lit up, if we pull a Now that the lights are lit up, if we pull a bulb out, what is going to happen?bulb out, what is going to happen?

Different wiring sizesDifferent wiring sizes

What are some common uses of the What are some common uses of the various wires displayed?various wires displayed?

Why would someone want larger wires? Why would someone want larger wires? Smaller wires?Smaller wires?

Why is a large wire used by power Why is a large wire used by power companies to bring electricity to your companies to bring electricity to your home when only small wire is needed to home when only small wire is needed to carry that same electricity to an appliance?carry that same electricity to an appliance?

Learning ObjectivesLearning Objectives

Explain series and parallel circuits, the Explain series and parallel circuits, the advantages and disadvantages of each, advantages and disadvantages of each, and how to connect series and parallel and how to connect series and parallel circuits.circuits.

Determine voltages for resistors in series Determine voltages for resistors in series and parallel circuits, and determine total and parallel circuits, and determine total current flowing through series and parallel current flowing through series and parallel circuits.circuits.

Learning ObjectivesLearning Objectives

Explain the mathematical relationship that Explain the mathematical relationship that exists in circuits containing more than one exists in circuits containing more than one resistor and use Ohm’s law in calculating resistor and use Ohm’s law in calculating current, resistance, or voltage for different current, resistance, or voltage for different circuits.circuits.

TermsTerms

AmpereAmpere Kirchoff’s First LawKirchoff’s First Law Kirchoff’s Second Kirchoff’s Second

LawLaw LoadLoad OhmOhm OhmmeterOhmmeter

Ohm’s LawOhm’s Law Parallel CircuitParallel Circuit ResistanceResistance Series CircuitSeries Circuit Series-Parallel CircuitSeries-Parallel Circuit VoltVolt

What are parallel and series What are parallel and series circuits?circuits?

The The series circuit series circuit is an electrical is an electrical connection method in which current flows connection method in which current flows through all devices in a circuit before through all devices in a circuit before returning to the source. returning to the source.

Series CircuitSeries CircuitSchematic DiagramSchematic Diagram

What are parallel and series What are parallel and series circuits?circuits?

A A parallel circuit parallel circuit is set up when the is set up when the resistors or capacitors are connected so resistors or capacitors are connected so as to allow current to divide and flow as to allow current to divide and flow through each individual device, then to through each individual device, then to combine and flow back to the source.combine and flow back to the source.

Parallel CircuitParallel CircuitSchematic DiagramSchematic Diagram

What are parallel and series What are parallel and series circuits?circuits?

The two types of circuits can be combined The two types of circuits can be combined to form a to form a series-parallel circuit. series-parallel circuit. This circuit has at least one resistor This circuit has at least one resistor

connected in series with at least two resistors connected in series with at least two resistors connected in parallel. connected in parallel.

The circuit is considered complete in its The circuit is considered complete in its loop or path when the current can flow loop or path when the current can flow through the through the load load before returning to the before returning to the source or point of origin.source or point of origin.

Series-Parallel CircuitSeries-Parallel CircuitSchematic DiagramSchematic Diagram

How do voltage and amperage How do voltage and amperage differ in their movement through differ in their movement through

series and parallel circuits?series and parallel circuits?

In a series circuit, voltage is divided between In a series circuit, voltage is divided between the devices connected in the circuit the devices connected in the circuit proportionately to the resistors. proportionately to the resistors. Each device in a series circuit receives the same Each device in a series circuit receives the same

amperage. amperage. There is only one path that the current flow may There is only one path that the current flow may

follow. follow.

How do voltage and amperage How do voltage and amperage differ in their movement through differ in their movement through

series and parallel circuits?series and parallel circuits?

By contrast, current may follow more than By contrast, current may follow more than one path in a parallel circuit. one path in a parallel circuit.

Current (amperage) can flow through any Current (amperage) can flow through any single device or all devices single device or all devices simultaneously.simultaneously.

Movement through parallel Movement through parallel circuits.circuits.

Devices connected in parallel receive the Devices connected in parallel receive the same voltage. same voltage.

However, the total current flowing through However, the total current flowing through a parallel circuit splits proportionately at a parallel circuit splits proportionately at each resistor and is equal to the sum of each resistor and is equal to the sum of the current flowing through each device.the current flowing through each device.

Kirchoff’s LawsKirchoff’s Laws

Kirchoff’s First Law Kirchoff’s First Law states that current states that current entering a junction is equal to the current entering a junction is equal to the current leaving the junction. leaving the junction.

Considering the behavior of voltage in Considering the behavior of voltage in these circuits, these circuits, Kirchoff’s Second Law Kirchoff’s Second Law follows up by stating that the sum of the follows up by stating that the sum of the voltage drops around a complete circuit voltage drops around a complete circuit loop or path is equal to the applied voltage loop or path is equal to the applied voltage to the circuit.to the circuit.

What is Ohm’s Law and how is it What is Ohm’s Law and how is it used to determine voltage, current, used to determine voltage, current,

and/or resistance for electrical and/or resistance for electrical circuits?circuits?

Ohm’s Law Ohm’s Law states that the current in an states that the current in an electrical circuit is directly proportional to electrical circuit is directly proportional to the amount of voltage which causes the the amount of voltage which causes the current to flow, and inversely proportional current to flow, and inversely proportional to the amount of resistance in the circuit.to the amount of resistance in the circuit.

Ohm’s LawOhm’s Law

One One volt volt (electrical pressure) is needed to (electrical pressure) is needed to push one push one ampere ampere (electrical current) (electrical current) through a conductor with one through a conductor with one ohm ohm (electrical resistance) of resistance. (electrical resistance) of resistance.

Resistance Resistance is the opposition to the flow of is the opposition to the flow of electrons.electrons.

Ohm’s Law (cont.)Ohm’s Law (cont.)

Ohm’s law can be mathematically Ohm’s law can be mathematically expressed as follows:expressed as follows:

Current = Current = Voltage Voltage or I = or I = EEResistance RResistance R

Where: Current = IWhere: Current = I Voltage = EVoltage = E Resistance = RResistance = R

Ohm’s Law (cont.)Ohm’s Law (cont.)

Examining the mathematical relationship, Examining the mathematical relationship, it is easy to see that as the voltage is it is easy to see that as the voltage is increased, the amount of current flowing in increased, the amount of current flowing in the circuit is increased. the circuit is increased.

If the amount of voltage is decreased, the If the amount of voltage is decreased, the amount of current flowing in the circuit is amount of current flowing in the circuit is decreased.decreased.

Ohm’s Law (cont.)Ohm’s Law (cont.)

The formula also shows that as the The formula also shows that as the resistance in the circuit is increased, the resistance in the circuit is increased, the amount of current in the circuit is amount of current in the circuit is decreased. decreased.

If the amount of resistance in the circuit is If the amount of resistance in the circuit is decreased, the amount of current in the decreased, the amount of current in the circuit is increased.circuit is increased.

Ohm’s Law (cont.)Ohm’s Law (cont.)

As the length of a conductor increases As the length of a conductor increases there is more resistance to the flow of there is more resistance to the flow of electricity along the conductor which electricity along the conductor which results in a drop in voltage. results in a drop in voltage.

The resistance of the circuit can easily be The resistance of the circuit can easily be measured across any device with an measured across any device with an ohmmeterohmmeter..

Ohm’s Law Circuit Schematic Ohm’s Law Circuit Schematic Diagram for Testing ResistorsDiagram for Testing Resistors

Review/SummaryReview/Summary

What are parallel and series circuits?What are parallel and series circuits?

How do voltage and amperage differ in How do voltage and amperage differ in their movement through series and parallel their movement through series and parallel circuits?circuits?

What is Ohm’s Law and how is it used to What is Ohm’s Law and how is it used to determine voltage, current, and/or determine voltage, current, and/or resistance for electrical circuits?resistance for electrical circuits?