Basic Electrical Theory and Magnetism Study Guide

1. ElectronicsIStudyGuide Follow the yellow brick road…. To a passing VOCATS score! Bill Sorenson, South Stanly High

2. X101 Basic Electrical Theory and Magnetism • Static electricity: static electricity is a building of electrical charge (electrons) on an object that is not electrically balanced. Think about dragging your feet on the carpet and then shocking your sibling. • Electrical work: Work happens when in an energy system, something causes something else to move or change shape. In electrical systems, electricity is converted to heat, light, sound pressure, etc. • Electrical Energy: Energy is the ability to do work. A water tower holds a lot of water with gravity pushing down on it. If you open a drain at the bottom, the energy causes the water to flow, which is work. In electrical systems the energy can be either electrical or magnetic or others.

3. Energy Levels • Two types of energy: POTENTIAL ENERGYand KINETIC ENERGY. • POTENTIAL ENERGY is defined as energy at rest, while KINETIC ENERGY is defined as energy at work. Think of it this way: a rock on top of a hill that is at rest, has Potential to do work. Once the rock begins to roll downhill, and is in motion, it is doing work. (Kinetic) A.S. WSHS

4. The Atom • The atom has three particles: • The proton, inside the nucleus, has a positive charge • The neutron, inside the nucleus, has NO charge properties • The electron, which orbit around the nucleus, are negative • ELECTRONS on the outer shell are called Valence electrons • They are the electrons that move to form electrical current. • The flow of electrons IS electricity!!!

5. What is electricity? • Current is the flow of electrons from atom to atom. Letter symbol is I, measured in amperes • Voltage is the force or pressure that causes flow when a path is available. Letter symbol is E or V, measured in volts. • Resistance is the opposition a material offers to that flow. Letter symbol is R, measured in ohms. • Conductance is the ability for flow that a material has. It’s the opposite of resistance. Letter symbol is G, measured in Siemans

6. Basic Electrical symbols, units • Visit the following website to Review basic electronic units • http://www.wisc-online.com/Objects/ViewObject.aspx?ID=ENG902

7. Magnetism • Magnetism is a natural force that causes certain materials to be attracted to others. • Magnetic attraction/repulsion is VERY similar to electromechanical attraction/repulsion • Magnetic terms • Permeability: ability of a magnet to store magnetic force • Flux: the lines of magnetic force • Pole: place in a magnet where lines of flux enter or leave the magnet • Lodestone: a naturally occurring magnet • Reluctance: Opposition a material offers to being magnetized • Ferromagnetic: materials that aid in developing magnetic fields.

8. Magnetism Continued • Magnets can be made using Electrical current looped into coils. • Placing an iron core in an electromagnet makes it much stronger. • Electronic devices utilize magnetism in a lot of different applications. Lines of force leave the north pole And enter the south. OPPOSITES LIKE ATTRACT REPEL

9. Magneto motive Force • Magnetic lines of force are created and can be used to actually move things. This is how many electrical motors work. By using electromagnets and fixed magnets, we can produce MECHANICAL energy from electrical. • The way this is done varies greatly.

10. X102 Electrical Safety • Risks of electrical work • Lasers: Many devices can damage your eyes • Fire: Excess current flow can cause fires • Class A: Combustibles, paper, wood, etc • Class B: Liquids, gas, kerosene, etc • Class C: Electrical/electronic fires • Class D: Burning metals, phosphorus, etc. • Shock: electrons moving through the body. • Burns, heart stoppage, muscle damage, death • .1 amp of current across your chest can be fatal • .01 amps you lose muscle control • .001 amps you feel a slight tingle

11. NFPA 70 Nat’l Fire Protection • National Fire and Protection Association • Sets NEC code for all wiring which the states use for state code • Set Fire prevention standards for all types of construction and electrical electronic codes. • Local codes may supersede state codes which may supersede NFPA codes, but only to be more stringent

12. FIRST Aid and Electronics Jobs • First aid for electrical shock • Remove Victim from source safely by turning off breaker or switch or using non conductive material • Treat for traumatic shock, elevate legs and keep warm • If needed administer CPR IF TRAINED • Treat burns by keeping them as clean as possible • GET HELP ASAP!

13. Multimeters: how they work • Multimeters are meters designed to measure the big three: Current, Voltage, and Resistance • See picture below Analog Meter Volt, ohm, milliameter Digital Meter

14. Analog Meters -VOM • Use a meter driven by a D’arsonval Movement. This uses the magnetic field generated by voltages to move the needle • Generally have to be Zero’d to measure ohms. Zero by touching leads together and adjusting ohms. • Usually have one or more amperage scales with jacks for each. • Meter scale is more difficult to read but can be highly accurate • Simpson 260 was the standard VOM for decades.

15. Digital Meters • Digital meters use digital readouts • Usually have jacks for volts/ohms and different amperage levels. • Range switch selects range of reading. • Function switch selects what you are measuring. • Do NOT require zeroing. • Measure RESISTANCE and VOLTAGE in parallel and Current in Series. • NEVER MEASURE RESISTANCE WITH POWER ON.

16. Light level, SPL, other meters • Light level meter: Measure amount of light present in lumens. Used to find optimal levels for pictures, videos, etc. • SPL meter: Measure sound pressure or noise in Db’s. Decibels are levels of sound relative to a specific noise level. • EMF or Gauss meter: Meter designed specifically to measure electromagnetic energy in a space.

17. Capacitors: BABY BATTERIES • A capacitor is simply two metal plates separated by some kind of insulator. • A capacitor stores a charge on those plates much like a battery. • A capacitor charges and discharges MUCH faster than a battery. • Capacitors are measured in FARADS, named after Faraday. • Capacitors are always measured in tiny units such as microfarads, pico farads. • Capacitors do NOT work like resistors mathematically. • Capacitors in parallel add up while in series they divide (the 1 over method for resistors)

18. Capacitors: what they look like Mylar Electrolytic Ceramic Disc

19. Capacitors: What they do • Capacitors store a charge. • Capacitors can be used to BLOCK low frequencies. • Capacitors are often used to manipulate AC waves in radio tuners and such. • Capacitors do NOT PASS DC current. • Capacitors are used to filter power supplies, they do this by smoothing out voltage. • Electrolytic capacitors that look like little cans can explode if hooked up backwards.

20. Capacitor Math • Capacitors in series act like resistors do in parallel. • 1/C1 + 1/ C2 = 1/CT • Capacitors in parallel add up. • C1 + C2 = CT ****IN AC Circuits the opposition Caps give is called Capacitive Reactance and its measured in Ohms. XC = opposition to changing AC in ohms

21. CapacitorColorCode • Used for very small caps that utilize a color code instead of digits. VALUES below in Pico farads

22. Reading Ceramic Disk Caps Values given in Pico farads. Pico farads are Trillionths (1/1,000,000,000,000) of a farad

23. SCHEMATICS for Capacitors

24. Resistors: They cause voltage drops • Resistors are devices designed to give resistance to manipulate voltages. • There are several types of resistors. • Resistors give off power in the form of heat. • Variable resistors are called potentiometers or rheostats. • Letter Symbol for Resistance is R. • Resistance is measured in Ohms.

25. Resistors: What they look like

26. Series Resistor Math • In series Resistors simply add up. • R1 + R2 + R3 = RT Total resistance

27. Resistors: Parallel Math • In parallel, the total opposition actually goes down so the formulae is: • 1/R1 + 1/R2 + 1/R3 = 1/RT • You can also use the product over sum method for just two resistors. • R1 x R2 Divided by R1 + R2

28. Resistors: The code • Many resistors are so small they use a color code to indicate their value. • The code is as follows: • First color is first digit • Second color is second digit • Third color is multiplier (or number of zeros) • Fourth color is tolerance (how accurate it is designed to be) usually 5% or 10%

29. Resistor color code example

30. SchematicsforResistors

31. Electrical Insulators • Insulators have an atomic structure that OPPOSES the flow of electricity. • Common insulators include: Rubber, Plastic, Glass, Ceramic, Paper • Insulators generally have 5 or more valence electrons in their outermost orbit. • Insulators are used to CONTAIN/DIRECT current.

32. Electrical Conductors • Conductors have an atomic structure that make them allow for current flow easily. • Most conductors are metals. • Good conductors generally have just one electron in the outermost shell, called the valence shell. • Conductors Route Electrical current • There are literally thousands of different types of conductors • All conductors have some resistance and the longer the wire, the more resistance. • Conductors CAN act as antenna as well so sometimes, they have to be grounded.

33. Types of Wire used as conductors • Conductors can be multi stranded wire or solid core. • Conductors can be made of copper, aluminum, or any other metal. • Wire is measured by feet or meters for length and by “GAUGE” for diameter of conductor. • The smaller the GAUGE, the BIGGER the wire. • #22 wire is small while #4 wire is bigger

34. American Wire Gauge

35. Switches • All a switch is really is just a device that can open a circuit by breaking a connection or make a circuit by connecting two conductors. • There are literally thousands of different types. • OPEN means OFF. • CLOSED means ON. • Open and closed are talking about the contacts, so open means no path for current and closed means a path exists.

36. Some examples of switches

37. Schematics for switches

38. FUSES: 1 time safety devices • Fuses are simply strips of conductive material designed to OPEN a circuit upon over current conditions. • FUSES PREVENT FIRES by limiting current to that which the circuit can safely handle. • Fuses are rated for voltage and more importantly CURRENT at which it opens. • Fast acting fuses are designed to open immediately. • Slow Blow fuses are designed to withstand short duration over current events. • Thermal fuses blow on HIGH temperature.

39. Fuses: Pix and schematics

40. FUSE SAFETY: • ALWAYS REMOVE POWER BEFORE REMOVING A FUSE! • NEVER REPLACE A FUSE WITH ONE RATED AT A HIGHER CURRENT OR LOWER VOLTAGE! • LETHAL VOLTAGES ARE PRESENT ACROSS THE CONNECTIONS OF A BLOWN FUSE! • IF A FUSE BLOWS TWICE, LOCATE THE SHORT IN THE CIRCUIT

41. If the fuse keeps blowing! • In a circuit that keeps blowing a fuse, the problem is a short circuit somewhere. • You can troubleshoot by placing a resistor in line with the power going to the fuse and then looking for component with zero voltage drop. • Always use extreme care when troubleshooting fuses as YOU could make the circuit if you bridge the fuse’s gap.

42. Circuit Breaker: Resettable fuse • A circuit breaker is designed to trip (OPEN) a circuit when too much current goes through it. • Circuit Breakers prevent fires! • Circuit Breakers are rated for current and trip current. • Some circuit breakers have visual indicators that show when they are tripped. • Find the cause of the breaker tripping before resetting.

43. How a circuit breaker works An over current condition causes the electromagnet to Pull the catch away from the other contact.

44. Batteries: We got the POWER! • A battery is physically two different metal plates separated by a chemical that causes one metal to give off electrons and the other to attract them. • There are hundreds of different types and sizes. • Batteries are rated in Voltage available and mAmps/Amps per hour they can deliver. • Many batteries pose explosion hazards when shorted or disposed of in fire. • The chemicals in many batteries pose health risks so they should NOT be thrown into landfills.

45. Typical Battery voltages SLA = Sealed Lead Acid, NiCD = Nickel Cadmium NiMh = Nickel Metal Hybrid, Li-on = Lithium Ion Li-polymer = Lithium Polymer

46. Battery Schematics and Pix Button Cell 3v Double AA 1.5 V Sealed Liquid Acid 12/24 V C battery 1.5V 9 V 3.6 V Cell phone battery

47. Battery Schematics and cells Cells are single battery units while many batteries come in manufactured packs. Example a Car battery has 6 Cells which add up to 12 Volts.

48. Ohm’s Law: The STUFF! • Ohm’s law is the relationship between Voltage (V), Current (I), and Resistance (R) • Voltage measured in volts is electrical FORCE or pressure. Also called POTENTIAL Difference • Current measured in Amperes is the actual FLOW of Electrons. • Resistance is the OPPOSITION to the flow of electrons.

49. Ohm’s law, the formulae Finding Current Example To find any one of the three, Cover it up and use the other two.

50. Ohm’s Law problem Problem #1 A 110 volt wall outlet supplies power to a strobe light with a resistance of 2200 ohms. How much current is flowing through the strobe light? • Choose your answer below • 0.5 amps • 2.0 amps • 0.05 amps • 1.0 amps