Unit 3 Lesson 5 AN INTRODUCTION TO ELECTRICAL

Unit 3 – Lesson 5 AN INTRODUCTION TO ELECTRICAL TECHNOLOGY

Electrical Technology Electrical technology is the technology of producing, storing, controlling, transmitting and getting work from electrical energy. (Example applications: power plant generator, flashlight, electric motor in a can opener, doorbell, electric heater, hair dryer. )

Electronic Technology Electronic technology as the technology of using small amounts of electricity for controlling; detecting; and information collecting, storing, retrieving, processing, and communicating. (Example applications: thermostat for controlling temperature, a metal detector, video tape recorder, computer, pocket calculator, telephone, radio, television. )

Important Concepts Resistance - The opposition to the flow of electrical charge. Conduction - The movement of electrically charged particles through a transmission medium. Conductor - A material containing many free electrons that move through the material easily.

Important Concepts Semi-conductor - Materials whose electrical conductivity can be precisely altered by appropriate manufacturing processes. A semiconductor behaves as an insulator at very low temperature, and has an appreciable electrical conductivity at room temperature although much lower conductivity than a conductor. Semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices. Such devices include transistors, solar cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits.

Important Concepts - Current - The force that moves electrons Direct Current - current that starts at one place and flows in one direction to the end destination, hence the name Direct. Alternating Current - current flows in one direction for a period of time and then switches direction, going the opposite way. It switches diretion over and over again continuously. In the united states the AC current in power lines goes switches direction, forward to backward, then backward to forward, 60 times each second. This is a frequency of 60 Hertz and is called 60 Hz AC electricity.

Important Concepts - Current One major reason for using ac rather than dc is the need for long range transmission. Transmission line power loss is proportional to the square of the current. To keep the current to a minimum while keeping the energy transmission at a high enough level it is necessary to use transformers. These raise the voltage to a very high level and lower the current accordingly. Direct current cannot be transformed so transmission would have to be at the low voltage safe for customer usage.

Important Concepts When electric generation first started (before 1900), there was competition between ac (Westinghouse) and dc (Edison). However the need for long distance transmission killed off the dc generation industry.

Important Concepts - Current Microelectronics use DC because they are composed, essentially, of transistors. Transistors are small "switches" which use voltages as control signals. If the control signals were changing polarity many times a second, the switches would open and close many times a second, leading to, well, a mess. It'd be very hard to make a digital computer which could use AC.

Important Concepts Voltage - the difference in the electrostatic charge that exists between two points. It is this imbalance in the electrostatic charge that causes electrons to flow from one point to the next. Known as potential difference.

Important Concepts Power - The rate of doing work or the rate of transferring energy Circuits - A complete path of an electric current including the source of electrical energy. Electric circuits provide a means of transferring and using electrical energy to produce heat, light, and sound as well as chemical changes.

Important Concepts Magnetism - A force that exists around magnets that attracts ferrous materials and is used in motors and generators. Ferrous materials - Ferrous is derived from the Latin term which means iron (hence the elemental symbol "Fe"). A non-ferrous metal is any metal which is not iron or any alloy of metals which does not contain iron as a component. Most (but not all) ferrous alloys are magnetic and even those which vary in magnetic attraction due to the amount of iron in the alloy. Stainless steel is not always magnetically attracted because the process of making it "stainless" removes a great deal of the iron (it is put in nitric acid to remove the iron leaving only a small amount of iron and mostly nickel).

Important Concepts Ohm’s law - The linear relationship between voltage and current through an electrical device. Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship: I = V/R

Important Concepts Ratio - The relationship in quantity, amount, or size between two or more things

Horsepower Horsepower calculation - James Watt performed experiments and determined that a horse could lift 550 pounds at a rate of one foot per second. Mechanical horsepower hp(I) ≡ 33, 000 ft-lbf/min = 550 ft·lbf/s = 745. 699872 W Metric horsepower hp(M) ≡ 75 kgf·m/s ≡ 735. 49875 W Electrical horsepower hp(E) ≡ 746 W Boiler horsepower hp(S) ≡ 33, 475 BTU/h = 9, 809. 5 W Hydraulic horsepower = flow rate (US gal/min) × pressure (psi) × 7/12, 000 or = flow rate (US gal/min) × pressure (psi) / 1714 = 550 ft·lbf/s = 745. 699872 W

Electromagnet – A core of magnetic material surrounded by a coil of wire through which an electric current is passed to magnetize the core.