1. Fundamentals of Electricity
CHAPTER
Fundamentals of Electricity 2
Instructor Name: (Your Name)

2. Learning Objectives
Relate electrical terms including voltage, current, and resistance to their hydraulic or pneumatic counterpart
Explain the relationship among voltage, current and resistance in an electrical circuit
Apply Ohm’s law to simple electrical circuits to determine an unknown voltage, current or resistance

3. Learning Objectives
Perform measurements of voltage, current and resistance using a digital multimeter (DMM)
Describe the concept of voltage drop across a resistance when current flows through the resistance
Demonstrate Kirchhoff’s voltage and current law through voltage and current measurements obtained from a series, a parallel, and a series-parallel circuit

4. Learning Objectives
Determine the total circuit resistance in a series, parallel, and series-parallel electrical circuit given the individual resistor values
Calculate voltage drops and currents draws in a series, parallel, and series-parallel circuit, given the individual resistor values and voltage source

5. Atoms, Protons and Electrons
Atoms are the smallest possible pieces of any known element
Atoms are made up of protons, electrons and neutrons
Protons have a positive charge and electrons have a negative charge
Like charges repel and opposite charges attract

6. Charges Suspended From Strings
Figure 2-6 Charges suspended from strings.

7. Atoms, Protons and Electrons
Atoms are like a solar system; protons are the sun with electrons orbiting like planets.
Figure 2-7 Copper Atom.

8. Displacing Electrons
Rubbing two dissimilar materials can strip electrons from one material and add them to the other
One material has a positive charge (missing electrons)
One material has a negative charge (too many electrons)
An atom with an unequal number of protons and electrons is called an ion

9. Displacing Electrons
A material with an excess of electrons or protons will attract a material with the opposite charge
An atom with more protons than electrons is a positive ion
An atom with more electrons than protons is a negative ion
Electrons flow from a location where there is extra electrons to a location that is missing electrons

10. Figure 2-8 Opposite charges on the paper and comb cause an attraction.

11. Electric Potential
Electric potential exists between two materials, one with excess electrons (negative charge) and one with an absence of electrons (positive charge)
Electric potential is know as voltage or electromotive force (EMF)
Voltage can be thought of as pressure in an electrical circuit
The unit of measurement of voltage or EMF is the volt
The symbol for volt is V (truck battery voltage is usually 12V)

12. Electron Flow The flow of electricity is known as electric current
Current flow is the number of electrons passing a stationary point in a given period of time
1 coulomb equals 6.25 billon-billion electrons passing a stationary point in a given period of time
Current is measured in amperes
The symbol for amperes is A

13. Direction of Current Flow
A battery has 2 terminals; positive and negative
The positive terminal is marked + and the negative is marked –
Conventional theory; positive to negative
Electron theory; negative to positive

14. Figure 2-9 Electron flow is like the movement of cars to the right, while conventional flow is like the movement of spaces to the left.

15. Direct and Alternating Current
Almost everything on a truck uses direct current (DC)
Direct current does not change direction or amplitude
Alternating current changes amplitude and direction of flow continually

16. Conductors
Conductors are made of materials that allow electron flow with little opposition
Conductors on trucks are usually made of copper
Free electrons are easily dislodged from the outer most band of an atom and into the outer most band of the atom next to it
The outer most band of an atom is called the valance band
Atom with one or two electrons in the valance band make good conductors

17. Figure 2-10 Electron flow is like marbles in a tube: a marble that enters the tube on the left is not the same marble that exits the tube on the right.

18. Conductors (continued)
Electron flow is believed to be an energy wave that flows through a conductor
The energy wave travels near the speed of light (186,000 miles/second)
The actual electrons only flow a few inches per hour
The energy wave is similar to the energy wave produced when a pool cue strikes a line of closely lined up pool balls and only the last ball rolls

19. Resistance
Resistance is the opposition to the flow of electric current
Ohm is the unit of measurement of electrical resistance
The symbol for ohms is the Greek letter omega (Ω)
Resistors are electrical components with a specific value of resistance

20. Wire Resistance
All electrical conductors have some resistance even though it may be a small amount
Wire resistance increases with the length of the wire, a 10mm wire has 10 times the resistance as a 1mm wire
A tungsten filament in a light bulb uses resistance to heat up and light when electrical current flows through it

21. Making Use of Wire Resistance
Figure 2-15 Electrical resistance cause heat and light when electric current flows through the light bulb filament.
Figure 2-14 Light bulb filament has a much smaller diameter than the wires connected to the light bulb causing an opposition to the flow of electric current.

22. Insulators
An insulator is a material that offers a great deal of resistance to the flow of electrical current
The resistance of an insulator is said to be very high
Insulators have five or more valence electrons
Plastic, rubber, and glass are examples of good insulators

23. Ohm’s Law
Increasing the voltage causes the electrical current flowing through a fixed value of resistance to increase
Increasing the resistance while keeping the voltage source held at a fixed value causes the electric current flowing through the resistance to decrease

24. Ohm’s Law (continued) Voltage ÷ Resistance=Current
1 Volt ÷ 1 Ohm = 1 ampere
E ÷ R = I
E = Voltage
R = Resistance
I = Amperes

25. Memorization Aid
Figure 2-16 Ohm’s law memorization aid.

26. Electrical Maps Circuits are the path that electrical current flows
Schematics are used to show the layout or relationship of electrical components
Schematics are also know as circuit diagrams or wiring diagrams
Electrical schematics use symbols to indicate electrical components found in an electrical circuit

27. Common Electrical Symbols
Figure 2-17 Electric symbols used to construct electrical schematic.

28. Measuring Pressure
Most pressure gauges display the difference between atmospheric pressure and the unknown pressure and reads as PSIG; G= Gauge
Some gauges display the difference between an absolute vacuum and the unknown pressure and reads as PSIA; A= Absolute
A differential pressure gauge measures the difference between two different gauge ports

29. Measuring Voltage
Voltmeters are electrical diagnostic tools that read voltage
Voltmeters display the difference in electrical potential (voltage) between two points
Most common volt meters are multimeters capable of reading volts, amperes and resistance
Test leads are wires with probes that connect the volt meter to the circuit being tested

30. Typical Multimeter
Figure 2-22 Digital multimeter.

31. Measuring Voltage (continued)
Test leads are typically colored red and black
The red lead is installed at the most positive point in the circuit
The black lead is installed at the most negative point in the circuit
Volt meters are connected to a circuit in parallel

32. Measuring Voltage With a Voltmeter
Figure 2-24 Measuring Voltage.

33. Measuring Current
Current flow through a circuit is measured with an ammeter
An ammeter is typically included in a multimeter
Ammeters are connected in series in a circuit
Most multimeters have a specific plug for reading current
The circuit current can not exceed the maximum amperage rating of the ammeter

34. Measuring Current With an Ammeter
Figure 2-26 Measuring current with an ammeter.

35. Tech Tip
Modern DMM are fantastic tools but have fooled almost every technician at one time or another. One reason for this is just a miniscule amount of voltage present in a circuit when resistance is being measured can result in dramatic resistance measurement errors. The miniscule voltage can be generated by engine coolant or water in contact with dissimilar metals, as will be explained in more detail in later chapters. If resistance measurements do not make sense, measure the voltage that is present between the two points of which you want to know the resistance. If the DMM displays any voltage, your resistance reading will not be accurate.

36. Current Shunts and Amp Probes
A current shunt is a known low value of resistance placed in the circuit.
Voltage is measured across the shunt
Current can be calculated with Ohm’s law
Clamp on current probes measure the strength of the magnetic field surrounding a wire and converts it to a current value
Current probes may also be designed as an input device to a DMM
Clamp on probes make troubleshooting easier because the circuit does not have to be opened to make a amperage reading

37. Clamp On Current Probes
Figure 2-28 Clamp-on current probes.

38. Measuring Resistance Resistance is measured with an ohmmeter
If the ohmmeter has a range setting, set to the highest range of unknown resistances
It is better to isolate the component from the rest of the circuit
If a negative resistance reading is obtained look for voltage on the circuit

39. A Pressure Differential Gauge
Figure 2-33 Using a differential pressure gauge.

40. Measuring Voltage and Current in a Series Circuit
Figure 2-40 Measuring voltage drop and current flow.

41. Increasing Resistance to 3 Ohms
Figure 2-41 Increasing resistance.

42. Measuring Voltage Drops
Figure 2-44 Difference in the voltage dropped across unequal series resistors.

43. Series Circuit Series circuits have only one path for current flow
The sum of all the voltage drops in a series circuit is equal to the source voltage
The total circuit resistance is the sum of all the resistance in the circuit

44. Parallel Circuits
Parallel circuits contain multiple paths for current flow
Voltage drops in a parallel circuit always equal the source voltage
The sum of the current flow in each branch of a parallel circuit is equal to the total current supplied by the voltage source
Adding additional parallel resistance decreases the total circuit resistance
Total circuit resistance in a parallel circuit is always less then the smallest resistor
To calculate total resistance in a parallel circuit use the product over the sum formula

45. Calculating Total Resistance in a Series Parallel Circuits
Figure 2-50 Solved series-parallel circuit.
Figure 2-49 Series-parallel simplification progression.

46. Metric Prefixes
Figure 2-51 Common metric prefixes used in electrical system troubleshooting.

47. Three Resistors in Parallel
Figure 2-52 Three resistors in parallel. Note the measured resistance value is less than any of the parallel-connected resistors.

48. Summary
A difference in electric potential between two points causes electrons to flow between the two points when a conductive pass is provided between them. Voltage is electrical potential and is measured in volts. Voltage can be thought of as pressure in a hydraulic or pneumatic circuit.
The flow of electrons is called current and measured in amperes. An ampere describes a quantity of electrons passing a stationary point per second. Electric current is like the fluid that flows in a hydraulic circuit.

49. Summary (continued)
The opposition of electric current flow is called resistance and is measured in ohms.
Ohm’s law mathematically describes the relationship between voltage, current, and resistance. Ohm’s law indicates that dividing the value of the voltage dropped across a resistance by the value of resistance in ohms yields the current flow through the resistance in amperes. Ohm’s law can be manipulated so that when any two quantities are known (voltage, current, or resistance) the third unknown quantity can be calculated.

50. Summary (continued)
A voltmeter is like a pressure differential gauge in that the difference in electrical potential between two points is being measured. A voltmeter is typically placed in parallel across a component to measure the voltage drop across the component.
An ammeter is like a flow meter in that the quantity of electrons passing a stationary point per second is being measured. An ammeter is always placed in series with the portion of the circuit that the current flow is being measured. Placing an ammeter in parallel with a component can damage the ammeter.

51. Summary (continued)
An ohmmeter measures resistance and is only used when there are no voltage sources in the circuit.
In a series electrical circuit, there is only one path for current to flow. The current is the same in a series circuit. The voltage dropped across components in a series circuit is proportional to the component’s resistance value relative to other components in that circuit.

52. Summary (continued)
In a parallel electrical circuit, there is more than one path for current flow. The circuit is divided among each parallel path. The greater the resistance of a path, the less current that flows through that path compared to other paths. The voltage dropped across each component in a parallel circuit is the same, regardless of the resistance of that component.

53. Summary (continued)
Series-parallel circuits have components that are connected in parallel and in series. The voltage drops and branch currents can be found by determining the equivalent resistance for the entire circuit. The equivalent resistance is then used to determine the total circuit current. The rules of series and parallel circuits are then applied to the circuit to determine the voltage drops and branch currents.