MElec-Ch1 - 1 Chapter 1 Properties of Electricity Properties of Electricity.
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Transcript of MElec-Ch1 - 1 Chapter 1 Properties of Electricity Properties of Electricity.
MElec-Ch1 - 1
Chapter 1Chapter 1
Properties of
Electricity
Properties of
Electricity
MElec-Ch1 - 2
OverviewOverview
• 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 ElectricityWhat 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 AnalogyWater 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 CircuitsElectrical Circuits
• Simple Series Circuit Same current flow through all devices
• Simple Series Circuit Same current flow through all devices
MElec-Ch1 - 6
Complex Series CircuitComplex 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 Off
MElec-Ch1 - 7
Complex Parallel CircuitComplex 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 On
MElec-Ch1 - 8
Ohm’s LawOhm’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 / I I = E / R
P = I * E P = I2 * R P = E2 / 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 / I I = E / R
P = I * E P = I2 * R P = E2 / R
EE
II RR
MElec-Ch1 - 9
Practice (fig 1-5)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 * R R = E / I R = 12 / 4
R = 3 ohms (or 3 Ω)
MElec-Ch1 - 10
Practice (fig 1-6)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 * R I = E / R I = 12 / 8
I = 1.5 amps
RT = R1 + R2
MElec-Ch1 - 11
Practice (fig 1-8)Practice (fig 1-8)
12 VDC
• What is current in each device?
6 amps in 2 ohms 2 amps in 6 ohms (each)
• What is total current?IT = I1 + I2 + I2 IT = 10 amps
2 Ohms 6 Ohms 6 Ohms
MElec-Ch1 - 12
Electrical PowerElectrical 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 / R I = 12 / 6 I = 2 amps
P = E * I P = 12 * 2 P = 24 watts
MElec-Ch1 - 13
What We Have Learned So Far
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-Ch1 - 14
Boat Circuit ProblemsBoat 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-Ch1 - 15
MultimetersMultimeters• 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-Ch1 - 16
Measuring VoltageMeasuring 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-Ch1 - 17
Measuring Voltage at Light
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-Ch1 - 18
Measuring Voltage DropMeasuring 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-Ch1 - 19
Measuring CurrentMeasuring 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-Ch1 - 20
Measuring ResistanceMeasuring 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-Ch1 - 21
Magnetic Lines of ForceMagnetic 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-Ch1 - 22
Remote Control CircuitRemote Control Circuit
AWG#2 (Large Wire)
AWG#16 (Small Wire)
Small current through solenoid coil- Controls larger current, through contacts, to Starter Motor
MElec-Ch1 - 23
SummarySummary
• 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-Ch1 - 24
Summary - 2Summary - 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