Electric CircuitsElectric Circuits

Mrs. CockrellMrs. Cockrell

PAP PhysicsPAP Physics

Electric CurrentElectric Current

Flow of electrical chargeFlow of electrical charge The rate at which electric charges The rate at which electric charges

move through a given area.move through a given area. FormulaFormula

I = q/tI = q/t I = current (A)I = current (A) q = charge (C)q = charge (C) t = time (s)t = time (s)

DC vs ACDC vs AC

Direct Current (DC)Direct Current (DC) All charges move in one direction from All charges move in one direction from

an area of high potential to an area of an area of high potential to an area of low potentiallow potential

Alternating Current (AC)Alternating Current (AC) Charges move back and forth Charges move back and forth

generating a flow of chargegenerating a flow of charge

Conventional Current vs Flow Conventional Current vs Flow of Electronsof Electrons

Conventional Current – Flow of Conventional Current – Flow of positive chargespositive charges

Flow of electrons – Movement of Flow of electrons – Movement of electronselectrons

They are opposite directions of each They are opposite directions of each otherother

Sources of CurrentSources of Current

Battery – Uses chemical energy to Battery – Uses chemical energy to generate DC currentgenerate DC current

Photovoltaic Cell (Solar Cell) – Photovoltaic Cell (Solar Cell) – Converts sunlight into DC currentConverts sunlight into DC current An inverter changes it to ACAn inverter changes it to AC

Generators – Converts kinetic energy Generators – Converts kinetic energy into AC.into AC.

Potential DifferencePotential Difference

Caused by a separation of opposite Caused by a separation of opposite chargescharges

Often times called Voltage or electric Often times called Voltage or electric potentialpotential

ResistanceResistance

The opposition to electron flow The opposition to electron flow through a conductorthrough a conductor

Resistance is affected by length, Resistance is affected by length, area, type of material, and area, type of material, and temperaturetemperature

Ohm’s LawOhm’s Law

FormulaFormula V = IRV = IR

V = Potential Difference (V)V = Potential Difference (V) I = Current (Amperes or Amps)I = Current (Amperes or Amps) R = Resistance (Ohm’s or R = Resistance (Ohm’s or ΩΩ))

ExampleExample A 1.5 V battery is connected to a small A 1.5 V battery is connected to a small

light bulb with a resistance of 3.5light bulb with a resistance of 3.5ΩΩ. . What is the current in the bulb?What is the current in the bulb?

Kilowatt-HourKilowatt-Hour

How electric companies charge for service.How electric companies charge for service. You pay for energy used, not power.You pay for energy used, not power.

1KW-Hr = 3.6 x 101KW-Hr = 3.6 x 1066 J J Example:Example:

A television set draws 2.0 A when operated on A television set draws 2.0 A when operated on 120 V. (A) How much power does the set use? 120 V. (A) How much power does the set use? (B) If the set is operated for an average of 7.0 (B) If the set is operated for an average of 7.0 h/day, what energy in kWh does it consume h/day, what energy in kWh does it consume per month? (30 days) (C) At 11 cents per kWh, per month? (30 days) (C) At 11 cents per kWh, what is the cost to operate the set per month?what is the cost to operate the set per month?

Electric CircuitsElectric Circuits

Set of electrical components connected so Set of electrical components connected so that they provide one or more complete that they provide one or more complete paths for the movement of chargespaths for the movement of charges Closed circuit – complete path, one in which Closed circuit – complete path, one in which

electrons are free to moveelectrons are free to move Open circuit – not a complete pathOpen circuit – not a complete path

Light Bulbs contain a complete conducting Light Bulbs contain a complete conducting pathpath

Diagramming a circuitDiagramming a circuit

Schematic DiagramSchematic Diagram Graphical Graphical

representation of representation of an electrical circuitan electrical circuit

Wire or Wire or ConductorConductor

ResistorResistor

Bulb or Bulb or LampLamp

PlugPlug

BatteryBattery

SwitchSwitch

CapacitorCapacitor

ExamplesExamples

Draw a schematic diagram of two Draw a schematic diagram of two resistors connect in a line with a resistors connect in a line with a battery.battery.

Series CircuitSeries Circuit

A circuit or portion of a circuit that A circuit or portion of a circuit that provides a single conducting path without provides a single conducting path without junctionsjunctions

Current through each resistor is the same Current through each resistor is the same but varying potential differencebut varying potential difference

Total Resistance (Equivalent Resistance) – Total Resistance (Equivalent Resistance) – sum of all resistancessum of all resistances

Sum of the voltages = total voltageSum of the voltages = total voltage All elements must be present to get All elements must be present to get

electron flowelectron flow

ExampleExample

A 9.0V battery is connected to four A 9.0V battery is connected to four light bulbs in series of resistances light bulbs in series of resistances 22ΩΩ, 4, 4ΩΩ, 5 , 5 ΩΩ, and 7 , and 7 ΩΩ. Draw the . Draw the schematic diagram and calculate the schematic diagram and calculate the equivalent resistance and current in equivalent resistance and current in the circuit.the circuit.

Parallel CircuitsParallel Circuits

Two or more components in a circuit that Two or more components in a circuit that are connected across common points or are connected across common points or junctions, providing separate paths for the junctions, providing separate paths for the current.current.

Resistors have the same potential Resistors have the same potential difference but varying currentsdifference but varying currents

Sum of the currents = total currentSum of the currents = total current Equivalent Resistance is calculated by Equivalent Resistance is calculated by

using the reciprocal relationshipusing the reciprocal relationship Not all elements must be present in order Not all elements must be present in order

to operateto operate

ExampleExample

A 9V battery is connected to four A 9V battery is connected to four resistors in parallel with the following resistors in parallel with the following resistances. 7 resistances. 7 ΩΩ, 5 , 5 ΩΩ, 4 , 4 ΩΩ, and 2 , and 2 ΩΩ. . Draw the schematic diagram and find Draw the schematic diagram and find the equivalent resistance for the the equivalent resistance for the circuit and the total current in the circuit and the total current in the circuit.circuit.

Complex CircuitsComplex Circuits

When wiring a home or building complex circuits When wiring a home or building complex circuits are used.are used.

Circuit breakers and fuses are placed in the Circuit breakers and fuses are placed in the circuits that open when the current becomes too circuits that open when the current becomes too high.high.

To calculate equivalent resistance, simplify the To calculate equivalent resistance, simplify the circuit into groups of series and complex circuitscircuit into groups of series and complex circuits

Then find equivalent resistances of each groupThen find equivalent resistances of each group Then work backwards to determine potential Then work backwards to determine potential

difference and currentdifference and current Mrs. Cockrell sample problemMrs. Cockrell sample problem

ExampleExample

A circuit is assembled such that a 6 A circuit is assembled such that a 6 ohm and 2 ohm in series with each ohm and 2 ohm in series with each other is in parallel with a 4 ohm other is in parallel with a 4 ohm resistor. This entire group is in series resistor. This entire group is in series with a 3 ohm resistor and a 6 ohm with a 3 ohm resistor and a 6 ohm resistor. Following the series/parallel resistor. Following the series/parallel group is a 1 ohm resistor. All attached group is a 1 ohm resistor. All attached to a 9V battery. Determine the current to a 9V battery. Determine the current in and potential difference across the 2 in and potential difference across the 2 ohm resistor.ohm resistor.

PowerPower

The rate at which energy is transferred.The rate at which energy is transferred. P=IVP=IV P = Power (W)P = Power (W) I = Current (A)I = Current (A) V = Electric Potential (V)V = Electric Potential (V)

Example:Example: A 6.0V battery delivers a 0.50 A current to an A 6.0V battery delivers a 0.50 A current to an

electric motor that is connected across its electric motor that is connected across its terminals. (A) what is the power of the motor? terminals. (A) what is the power of the motor? (B) If the motor runs for 5.0 minutes, how much (B) If the motor runs for 5.0 minutes, how much energy is delivered?energy is delivered?