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Chapter 1Chapter 1

Properties of

Electricity

Properties of

Electricity

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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

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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

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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

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Electrical CircuitsElectrical Circuits

• Simple Series Circuit Same current flow through all devices

• Simple Series Circuit Same current flow through all devices

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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

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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

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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

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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)

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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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

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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

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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