PSAA Curriculum Unit Physical Science Systems

Problem Area Energy and Power Systems

Resistance in Series and Parallel Circuits Lesson

Christmas Lights… Series or Parallel Circuits? Before plugging in the lights, which string is connected in series and which one is connected in parallel? Before plugging in the lights, which string is connected in series and which one is connected in parallel? Now that the lights are lit up, if we pull a bulb out, what is going to happen? Now that the lights are lit up, if we pull a bulb out, what is going to happen?

Different wiring sizes What are some common uses of the various wires displayed? What are some common uses of the various wires displayed? Why would someone want larger wires? Smaller wires? Why would someone want larger wires? Smaller wires? Why is a large wire used by power companies to bring electricity to your home when only small wire is needed to carry that same electricity to an appliance? Why is a large wire used by power companies to bring electricity to your home when only small wire is needed to carry that same electricity to an appliance?

Learning Objectives Explain series and parallel circuits, the advantages and disadvantages of each, and how to connect series and parallel circuits. Explain series and parallel circuits, the advantages and disadvantages of each, and how to connect series and parallel circuits. Determine voltages for resistors in series and parallel circuits, and determine total current flowing through series and parallel circuits. Determine voltages for resistors in series and parallel circuits, and determine total current flowing through series and parallel circuits.

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

Terms Ampere Ampere Kirchoffs First Law Kirchoffs First Law Kirchoffs Second Law Kirchoffs Second Law Load Load Ohm Ohm Ohmmeter Ohmmeter Ohms Law Ohms Law Parallel Circuit Parallel Circuit Resistance Resistance Series Circuit Series Circuit Series-Parallel Circuit Series-Parallel Circuit Volt Volt

What are parallel and series circuits? The series circuit is an electrical connection method in which current flows through all devices in a circuit before returning to the source. The series circuit is an electrical connection method in which current flows through all devices in a circuit before returning to the source.

Series Circuit Schematic Diagram

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

Parallel Circuit Schematic Diagram

What are parallel and series circuits? The two types of circuits can be combined to form a series-parallel circuit. The two types of circuits can be combined to form a series-parallel circuit. This circuit has at least one resistor connected in series with at least two resistors connected in parallel. This circuit has at least one resistor connected in series with at least two resistors connected in parallel. The circuit is considered complete in its loop or path when the current can flow through the load before returning to the source or point of origin. The circuit is considered complete in its loop or path when the current can flow through the load before returning to the source or point of origin.

Series-Parallel Circuit Schematic Diagram

How do voltage and amperage differ in their movement through series and parallel circuits? In a series circuit, voltage is divided between the devices connected in the circuit proportionately to the resistors. In a series circuit, voltage is divided between the devices connected in the circuit proportionately to the resistors. Each device in a series circuit receives the same amperage. Each device in a series circuit receives the same amperage. There is only one path that the current flow may follow. There is only one path that the current flow may follow.

How do voltage and amperage differ in their movement through series and parallel circuits? By contrast, current may follow more than one path in a parallel circuit. By contrast, current may follow more than one path in a parallel circuit. Current (amperage) can flow through any single device or all devices simultaneously. Current (amperage) can flow through any single device or all devices simultaneously.

Movement through parallel circuits. Devices connected in parallel receive the same voltage. Devices connected in parallel receive the same voltage. However, the total current flowing through a parallel circuit splits proportionately at each resistor and is equal to the sum of the current flowing through each device. However, the total current flowing through a parallel circuit splits proportionately at each resistor and is equal to the sum of the current flowing through each device.

Kirchoffs Laws Kirchoffs First Law states that current entering a junction is equal to the current leaving the junction. Kirchoffs First Law states that current entering a junction is equal to the current leaving the junction. Considering the behavior of voltage in these circuits, Kirchoffs Second Law follows up by stating that the sum of the voltage drops around a complete circuit loop or path is equal to the applied voltage to the circuit. Considering the behavior of voltage in these circuits, Kirchoffs Second Law follows up by stating that the sum of the voltage drops around a complete circuit loop or path is equal to the applied voltage to the circuit.

What is Ohms Law and how is it used to determine voltage, current, and/or resistance for electrical circuits? Ohms Law states that the current in an electrical circuit is directly proportional to the amount of voltage which causes the current to flow, and inversely proportional to the amount of resistance in the circuit. Ohms Law states that the current in an electrical circuit is directly proportional to the amount of voltage which causes the current to flow, and inversely proportional to the amount of resistance in the circuit.

Ohms Law One volt (electrical pressure) is needed to push one ampere (electrical current) through a conductor with one ohm (electrical resistance) of resistance. One volt (electrical pressure) is needed to push one ampere (electrical current) through a conductor with one ohm (electrical resistance) of resistance. Resistance is the opposition to the flow of electrons. Resistance is the opposition to the flow of electrons.

Ohms Law (cont.) Ohms law can be mathematically expressed as follows: Ohms law can be mathematically expressed as follows: Current = Voltage or I = E Resistance R Where: Current = I Voltage = E Voltage = E Resistance = R Resistance = R

Ohms Law (cont.) Examining the mathematical relationship, it is easy to see that as the voltage is increased, the amount of current flowing in the circuit is increased. Examining the mathematical relationship, it is easy to see that as the voltage is increased, the amount of current flowing in the circuit is increased. If the amount of voltage is decreased, the amount of current flowing in the circuit is decreased. If the amount of voltage is decreased, the amount of current flowing in the circuit is decreased.

Ohms Law (cont.) The formula also shows that as the resistance in the circuit is increased, the amount of current in the circuit is decreased. The formula also shows that as the resistance in the circuit is increased, the amount of current in the circuit is decreased. If the amount of resistance in the circuit is decreased, the amount of current in the circuit is increased. If the amount of resistance in the circuit is decreased, the amount of current in the circuit is increased.

Ohms Law (cont.) As the length of a conductor increases there is more resistance to the flow of electricity along the conductor which results in a drop in voltage. As the length of a conductor increases there is more resistance to the flow of electricity along the conductor which results in a drop in voltage. The resistance of the circuit can easily be measured across any device with an ohmmeter. The resistance of the circuit can easily be measured across any device with an ohmmeter.

Ohms Law Circuit Schematic Diagram for Testing Resistors

Review/Summary What are parallel and series circuits? What are parallel and series circuits? How do voltage and amperage differ in their movement through series and parallel circuits? How do voltage and amperage differ in their movement through series and parallel circuits? What is Ohms Law and how is it used to determine voltage, current, and/or resistance for electrical circuits? What is Ohms Law and how is it used to determine voltage, current, and/or resistance for electrical circuits?