NCCER 26103-11 MIX

NCCERElectricalOHMS LAW

NCCER 26103-11 MIX

Created 3 years ago

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Slide Content
1. Slide 2 - Objectives

• When trainees have completed this session, they should be able to do the following:
• 1. Define voltage and identify the ways in which it can be produced.
• 2. Explain the difference between conductors and insulators.
• 3. Define the units of measurement that are used to measure the properties of electricity.
• 4. Identify the meters used to measure voltage, current, and resistance.
• 5. Explain the basic characteristics of series and parallel circuits.
• This is a knowledge-based module; there are no Performance Tasks.
• Introduction to Electrical Circuits 26103-14
2. Slide 3 - 1.0.0

• Introduction to Electrical Circuits 26103-14
• Introduction
• • A basic electrical circuit contains a voltage source, a load, and conductors to carry the current.
• • Current flow (in amps) is affected by the resistance (in ohms) presented by the load.
• • The amount of energy consumed by a load is often expressed in watts (W).
3. Slide 4 - 2.0.0 – 2.1.2

• Introduction to Electrical Circuits 26103-14
• Atomic Theory
• The nucleus of an atom contains one or more positive particles (protons) and is orbited by one or more negative particles (electrons).
4. Slide 5 - 2.0.0 – 2.1.2

• Introduction to Electrical Circuits 26103-14
• Electrical Charges
• Like charges repel one another, while unlike charges attract one another. This is known as the Law of Electrical Charges.
5. Slide 6 - 2.2.0

• Introduction to Electrical Circuits 26103-14
• Conductors and Insulators
• • Whether or not a substance is a good conductor or insulator depends on the number of electrons in the outermost (valence) shell of an the atom.
• • A conductor has three or fewer electrons in the outer shell, an insulator has five or more, and a semiconductor has four.
6. Slide 7 - 2.2.0

• Conductors normally have 3 or less Valence electrons.
• Introduction to Electrical Circuits 26103-14
7. Slide 8 - 2.2.0

• Semiconductors normally have 4 Valence electrons.
• Introduction to Electrical Circuits 26103-14
8. Slide 9 - 2.2.0

• Insulators normally has 5 or more Valence Electrons
• Introduction to Electrical Circuits 26103-14
9. Slide 10 - 2.3.0

• Introduction to Electrical Circuits 26103-14
• Magnetism
• • Magnetic fields are used to operate motors, relays, transformers, and solenoids.
• • Magnetic objects have a north and south pole. Opposing poles attract while like poles repel.
10. Slide 11 - 2.3.0

• Introduction to Electrical Circuits 26103-14
• Electromagnet
• • Current flow through a conductor produces a magnetic field. When wrapped around an iron bar, it produces an electromagnet.
• • The opposing forces in a rotating magnetic field can be used to turn a motor.
11. Slide 12 - 3.0.0

• Introduction to Electrical Circuits 26103-14
• Electrical Power Generation and Distribution
• • Electric power can be generated using coal-burning, nuclear, hydroelectric, solar, and wind power plants.
• • Power is stepped up for transmission and stepped down for distribution to the end user using transformers.
12. Slide 13 - 3.0.0

• Introduction to Electrical Circuits 26103-14
• Internal Power Distribution
• • The typical residence receives voltage at 240 volts (V), which is used to operate large appliances such as stoves and clothes dryers. Small appliances such as toasters and hair dryers operate on 120V.
• • Commercial power is typically three-phase and supplied at 208V, 480V, or 575V.
13. Slide 14 - 4.0.0 – 4.3.1

• Introduction to Electrical Circuits 26103-14
• Electric Charge and Current
• • The ability of a charge to do work is called potential. The sum of the electrical charges in a field is the electromotive force (emf) or voltage (V), which is expressed in equations as E.
• • Electric charge is measured in coulombs.
• • A battery creates an electric charge by chemically producing free electrons at its negative terminal.
14. Slide 15 - 4.2.0

• Voltage is defined as, “The force that causes electrons to move”
• It is also called electromotive force
• Introduction to Electrical Circuits 26103-14
15. Slide 16 - 4.0.0 – 4.3.1

• Introduction to Electrical Circuits 26103-14
• Conductor Properties
• • Current flow is measured in amps (A) and the intensity of current flow is represented in equations by the letter I.
• • Resistance is the opposition to current flow. It is measured in ohms (Ω) and represented in equations by the letter R. The hotter a wire, the greater its resistance.
• Next Session…
• Ohm’s Law
16. Slide 17 - 5.0.0

• Introduction to Electrical Circuits 26103-14
• Ohm’s Law
• • Ohm’s law defines the relationships between voltage (E), current (I), and resistance (R).
• • The formula can be rearranged to find any of the three values.
17. Slide 18 - 5.0.0

• Current – in a series circuit is = to the V applied to the circuit ÷by the resistance.
• Resistance – in a series circuit is = to the V applied to the circuit ÷ by the current.
• Voltage – in a series circuit is = to the current ×by the resistance.
• Introduction to Electrical Circuits 26103-14

19. Slide 20 - 6.0.0

• Introduction to Electrical Circuits 26103-14
20. Slide 21 - 6.0.0

• Introduction to Electrical Circuits 26103-14
21. Slide 22

• Introduction to Electrical Circuits 26103-14
22. Slide 23 - 6.0.0

• Introduction to Electrical Circuits 26103-14
• Schematic Representation of Circuit Elements
• A schematic diagram shows circuit paths and components using lines and symbols.
23. Slide 24 - 6.0.0

• Introduction to Electrical Circuits 26103-14
• Standard Schematic Symbols
24. Slide 25 - 7.0.0 – 7.1.0

• Introduction to Electrical Circuits 26103-14
• Resistors
• • Resistors are typically made of nickel resistance wire covered in porcelain.
• • Fixed resistors are the most common, but variable resistors are also available.
25. Slide 26 - 7.0.0 – 7.1.0

• Introduction to Electrical Circuits 26103-14
• Symbols Used for Variable Resistors
• • Variable resistors include rheostats (such as dimmers) and potentiometers.
• • The resistance is adjusted using a movable contact.
26. Slide 27 - 7.0.0 – 7.1.0

• Introduction to Electrical Circuits 26103-14
• Resistor Color Codes
• Resistors are color-coded to show their value.
27. Slide 28 - 7.0.0 – 7.1.0

• Introduction to Electrical Circuits 26103-14
• Sample Color Codes on a Fixed Resistor
• • Brown = 1, black = 0, red = 2 zeros, gold = tolerance of +/-5%.
• • This resistor has a value of 1,000Ω, +/-5%.
28. Slide 29 - 8.0.0 – 8.3.0

• Introduction to Electrical Circuits 26103-14
• Electrical Circuits
• • Circuits can be categorized by the way in which the loads are connected.
• • Common connections include series, parallel, and series-parallel. Most household circuits are wired in parallel.
• • The type of circuit determines the method used to calculate the resistance.
29. Slide 30 - 8.1.0

• In a Series circuit, the Total Resistance = the SUM of the individual resistors.
• Introduction to Electrical Circuits 26103-14

31. Slide 32 - 8.2.0

• In a Parallel circuit, each resistor sees the same voltage.
• Introduction to Electrical Circuits 26103-14
32. Slide 33

• Introduction to Electrical Circuits 26103-14
33. Slide 34 - 8.2.0

• In a Parallel circuit, each resistor sees the same voltage, BUT uses a different formula to calculate RESISTANCE.
• Introduction to Electrical Circuits 26103-14
34. Slide 35

• Introduction to Electrical Circuits 26103-14
35. Slide 36 - 9.0.0

• Introduction to Electrical Circuits 26103-14
• Electrical Measuring Instruments
• The most common test meter is the volt-ohm-milliammeter (VOM). Both analog and digital versions are available.
36. Slide 37 - 9.0.0

• Introduction to Electrical Circuits 26103-14
• Clamp-On Ammeter
• • A clamp-on ammeter is used to measure the current through a conductor by clamping the jaws of the meter around the wire.
• • The magnetic field created by the current in the conductor is then measured by the meter.
37. Slide 38 - 9.1.0

• Introduction to Electrical Circuits 26103-14
• Measuring Current
• • Do not use a clamp-on ammeter with dirty or misaligned jaws.
• • Use the meter on only one conductor at a time.
38. Slide 39 - 9.1.0

• Introduction to Electrical Circuits 26103-14
• In-Line Ammeter Test Setup
• Inline ammeters are connected in series with the circuit and are much less common because they require the circuit to be opened.
39. Slide 40 - 9.2.0

• Introduction to Electrical Circuits 26103-14
• Measuring Voltage
• • A voltmeter is connected in parallel with (across) the component or circuit to be tested to check whether the correct voltage is being supplied.
• • Like an ammeter, a voltmeter is used with the power on.
40. Slide 41 - 9.3.0

• Introduction to Electrical Circuits 26103-14
• Measuring Resistance
• • Resistance is measured using an ohmmeter with the power to the circuit shut off.
• • Ohmmeters can be used to check the resistance of motor windings and to check for electrical continuity in a circuit.
41. Slide 42 - 9.3.0

• Introduction to Electrical Circuits 26103-14
• Continuity Tester
• • A simple continuity tester can also be used to check for continuity or to identify multiple wires in a circuit.
• • A continuity tester uses a beep and/or light to indicate a continuous circuit. If there is no signal, the circuit is open.
42. Slide 43 - 9.4.0

• Introduction to Electrical Circuits 26103-14
• Voltage Testers
• • Voltage testers can be used to check for the presence of voltage when troubleshooting a circuit or to make sure the voltage is off before handling components.
• • Voltage testers typically only show the presence/absence of voltage and are not meant for precise circuit measurements.
• Next Session…
• Electrical Power
43. Slide 44 - 10.0.0

• Introduction to Electrical Circuits 26103-14
• Electrical Power
• • Power is defined as the rate of doing work or the energy used. Electrical power is measured in joules (J). One watt (W) is the measure of the number of joules per second (J/s).
• • One watt is also equal to one ampere of current flowing through a potential difference of one volt.
44. Slide 45 - 10.0.0

• Introduction to Electrical Circuits 26103-14
• Conversion Table
• • Mechanical power is measured in terms of horsepower (hp).
• • To convert horsepower to watts, multiply by 746. For example, a 2hp motor draws 1,492W.
• • A kilowatt (kW) is equal to 1,000W.
45. Slide 46 - 10.1.0

• Power is = amps X volts
• P = I X V
• Introduction to Electrical Circuits 26103-14
46. Slide 47

• Introduction to Electrical Circuits 26103-14
47. Slide 48 - 10.1.0 – 10.2.0

• Introduction to Electrical Circuits 26103-14
• • Power is calculated using the formula: Power (P) = Current (I) x Voltage (E). The formula can be rearranged to find any unknown value.
• • Resistors are given power ratings to show how much heat the resistor can withstand before burning out.
• Power Equation; Power Rating of Resistors
48. Slide 49 - Wrap Up

• 3-2-1
• 3 – Write 3 important things learned during class
• 2 – Write 2 questions you have about the material