MElec-Ch1 - 1 Chapter 1 Properties of Electricity Properties of Electricity

MElec-Ch1 - 2 Overview What is Electricity Ohm’s Law Boat Circuit Problems Multimeters Magnetic Lines of Force What is Electricity Ohm’s Law Boat Circuit Problems Multimeters Magnetic Lines of Force

MElec-Ch1 - 3 What is Electricity Electricity consists of electrons  Negatively charged  Electrons actually flow from negative to positive Current “flow”, by convention, from positive to negative Conductors have electrons that readily move  e.g. silver, copper, metal and liquids (salt water) Insulation has tightly bonded electrons  Charges do NOT move  e.g. plastic, rubber, glass and ceramics Electricity consists of electrons  Negatively charged  Electrons actually flow from negative to positive Current “flow”, by convention, from positive to negative Conductors have electrons that readily move  e.g. silver, copper, metal and liquids (salt water) Insulation has tightly bonded electrons  Charges do NOT move  e.g. plastic, rubber, glass and ceramics

MElec-Ch1 - 4 Water Analogy Height of water = Voltage Valve = Switch Water wheel = Electric motor Small pipe = Resistance Height of water = Voltage Valve = Switch Water wheel = Electric motor Small pipe = Resistance

MElec-Ch1 - 5 Electrical Circuits Simple Series Circuit  Same current flow through all devices Simple Series Circuit  Same current flow through all devices

MElec-Ch1 - 6 Complex Series Circuit If one light bulb burns out…  No lights will be on  Therefore, not used for light circuits If one light bulb burns out…  No lights will be on  Therefore, not used for light circuits Off

MElec-Ch1 - 7 Complex Parallel Circuit If one light bulb burns out…  Other will remain on  Therefore, used for light circuits If one light bulb burns out…  Other will remain on  Therefore, used for light circuits On

MElec-Ch1 - 8 Ohm’s Law E=Voltage (pressure) in volts I=Current (rate of flow) in amperes R=Resistance (friction) in ohms P=Power (work) in watts E = I * R R = E / II = E / R P = I * EP = I 2 * R P = E 2 / R E=Voltage (pressure) in volts I=Current (rate of flow) in amperes R=Resistance (friction) in ohms P=Power (work) in watts E = I * R R = E / II = E / R P = I * EP = I 2 * R P = E 2 / R E E I I R R

MElec-Ch1 - 9 Practice (fig 1-5) Given 12 volts and 4 amps What is resistance? Given 12 volts and 4 amps What is resistance? 12 VDC 4.0 Amps E = I * RR = E / IR = 12 / 4 R = 3 ohms (or 3 Ω)

MElec-Ch Practice (fig 1-6) Given 12 volts and 8 ohms What is current? Given 12 volts and 8 ohms What is current? 12 VDC 4 ohms (each) E = I * RI = E / RI = 12 / 8 I = 1.5 amps R T = R 1 + R 2

MElec-Ch Practice (fig 1-8) 12 VDC What is current in each device? 6 amps in 2 ohms2 amps in 6 ohms (each) What is total current? I T = I 1 + I 2 + I 2 I T = 10 amps 2 Ohms 6 Ohms

MElec-Ch Electrical Power Watt is unit of electrical power Given 12 VDC and total resistance of 6 Ω What is total power? Watt is unit of electrical power Given 12 VDC and total resistance of 6 Ω What is total power? I = E / RI = 12 / 6I = 2 amps P = E * IP = 12 * 2 P = 24 watts

MElec-Ch What We Have Learned So Far Electricity is the negatively charged electrons that have been freed from the structure of an atom For electricity to perform some useful function it must flow in a circuit There are two basic types of electrical circuits  The Series Circuit  The Parallel Circuit Using Ohm's Law we can calculate the three electrical values in a circuit, i.e. Voltage, Amperage, and Resistance The fourth electrical value is Power  Power is measured in Watts  Using the PIE equation we can calculate Power  Using Ohm's Law and PIE equation if we know any two values we can find the other two Electricity is the negatively charged electrons that have been freed from the structure of an atom For electricity to perform some useful function it must flow in a circuit There are two basic types of electrical circuits  The Series Circuit  The Parallel Circuit Using Ohm's Law we can calculate the three electrical values in a circuit, i.e. Voltage, Amperage, and Resistance The fourth electrical value is Power  Power is measured in Watts  Using the PIE equation we can calculate Power  Using Ohm's Law and PIE equation if we know any two values we can find the other two

MElec-Ch Boat Circuit Problems Open Circuit is “break” in electrical wiring  Current flow (path) is interrupted Sometimes deliberately by switch Short circuit is electrical wiring shortened from original length  Shorts to ground  Interwiring short  Internal short Open Circuit is “break” in electrical wiring  Current flow (path) is interrupted Sometimes deliberately by switch Short circuit is electrical wiring shortened from original length  Shorts to ground  Interwiring short  Internal short

MElec-Ch Multimeters Used to measure  Voltage  Current  Resistance Types of Multimeters  Analog  Digital Preferred Easier to read Used to measure  Voltage  Current  Resistance Types of Multimeters  Analog  Digital Preferred Easier to read

MElec-Ch Measuring Voltage  Voltage to DC  Range to 20 volts  Red lead to positive  Black lead to negative  Meter across load Parallel with load Battery voltage is 12.6  Voltage to DC  Range to 20 volts  Red lead to positive  Black lead to negative  Meter across load Parallel with load Battery voltage is 12.6

MElec-Ch Measuring Voltage at Light  with good fuse  and switch “On” Should measure approx. 12 VDC at each light  with good fuse  and switch “On” Should measure approx. 12 VDC at each light

MElec-Ch Measuring Voltage Drop Across a closed switch  Should measure zero volts Across a high resistance “connection”  Should measure a voltage drop Across a closed switch  Should measure zero volts Across a high resistance “connection”  Should measure a voltage drop

MElec-Ch Measuring Current  Current to DC  Range to 10 amps  Red lead to current jack on multimeter  Insert meter in series with circuit  Current to DC  Range to 10 amps  Red lead to current jack on multimeter  Insert meter in series with circuit When measuring voltage - meter is across the load

MElec-Ch Measuring Resistance  Function to resistance  Touch test leads together  Adjust resistance to zero (0.0) ohms  Place test leads across device to be measured Continuity measurement  When test leads are across low resistance (Good circuit or device)  Will hear a buzz indicating continuity  Function to resistance  Touch test leads together  Adjust resistance to zero (0.0) ohms  Place test leads across device to be measured Continuity measurement  When test leads are across low resistance (Good circuit or device)  Will hear a buzz indicating continuity

MElec-Ch Magnetic Lines of Force Results of Electrical Current  Heat (due to resistance in wire)  Chemical reaction (in current carrying solution)  Magnetic Field (illustrated) Results of Electrical Current  Heat (due to resistance in wire)  Chemical reaction (in current carrying solution)  Magnetic Field (illustrated)

MElec-Ch Remote Control Circuit AWG#2 (Large Wire) AWG#16 (Small Wire) Small current through solenoid coil - Controls larger current, through contacts, to Starter Motor

MElec-Ch Summary Electricity is negatively charged electrons Current flows from positive to negative Types of circuits  Series (one path for current flow)  Parallel (multiple paths for current flow) Ohm’s Law  E = I * R  P = E * I Boat Circuit Problems  Open Circuits  Short Circuits Electricity is negatively charged electrons Current flows from positive to negative Types of circuits  Series (one path for current flow)  Parallel (multiple paths for current flow) Ohm’s Law  E = I * R  P = E * I Boat Circuit Problems  Open Circuits  Short Circuits

MElec-Ch Summary - 2 Multimeter  Digital preferred  Measure voltage across (parallel to) load Can also measure voltage drop  Measure current in series with load Magnetic Lines of Force  Concentrated in coil  Solenoids use in remote control circuits Small current controls large current Multimeter  Digital preferred  Measure voltage across (parallel to) load Can also measure voltage drop  Measure current in series with load Magnetic Lines of Force  Concentrated in coil  Solenoids use in remote control circuits Small current controls large current