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Download U3e Test Review Electrical Technology 1
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TEST REVIEW ELECTRONS • • • • • • Electricity begins with Electrons. ATOMS Electron cloud surrounds an atom’s nucleus Nucleus is made of Protons and Neutrons Electrons – negative charge Protons – positive charge Neutrons – zero charge (neutral) U3e-L1 REVIEW CIRCUITS • • The paths that electrons travel are called circuits. Circuits must consist of three things: • Power Source – with positive and negative terminals. ELECTRONS move • Conductor – the path the from negative ( ) electrons travel along. • Load terminal – this is what to the electricity powers ((e.g. positive + )motor, light bulb) terminal LOAD U3e-L1 REVIEW CONDUCTORS • • • Conduct – from Latin for “leading, guiding.” A conductor is any material that allows electrons to easily flow. Remember the atom: – – • • Conductors’ electrons are not tightly bound to the atom. Conductors have free electrons. Which material has free electrons, Wood or Metal? Metals conduct electricity easily. U3e-L1 Review INSULATORS • • • Insulate – from Latin for “separate, divided.” An insulator is any material that impedes the flow of electrons. Remember the atom: – – • • Insulators’ electrons are tightly bound to the atom. Because the electrons don’t move, insulators cannot conduct electricity very well, if at all. Which material has bound electrons, Wood or Metal? Wood does not have free electrons. U3e-L1 Bound Free-electrons Aluminum Copper Plastic Cotton Wood Silver Gold Air Electrons INSULATOR CONDUCTOR Cotton Wood Plastic Air Copper Gold Silver Aluminum BOUND ELECTRONS FREE ELECTRONS U3e-L1 Review Joule’s Law • James Joule (1818 – 1889) – showed that heat and electrical energy are interchangeable. • Joule’s Law: Power = Voltage x Current P=VI Watts = Volts x Amperes U3e-L1 Review Ohm’s Law • George Ohm (1789 – 1854) – a high school and university mathematics instructor • Discovered ~1827 • Voltage = Current x Resistance V=IR What are the units of this formula? Volts = Amperes x Ohms U3e-L1 TERMINOLOGY • Current (I) – the motion of electrons from one atom to the next in a material. – In our circuit, electrons flow from ___________ NEGATIVE terminal to the ___________terminal. POSITIVE – This motion of electrons through our conductor (wire) is considered current (like water through a pipe). • Materials that resist current are called INSULATORS ___________. • Materials that provide LOAD a path for current are called ___________. CONDUCTORS • Current is measured in AMPERES (Amps) U3e-L2 Review TERMINOLOGY • Voltage (V) – the electric potential between two points of opposite charge. • Voltage is the potential energy of the electrical power source. • Voltage is measured in Volts (V). U3e-L2 Review Electric Schematics 1. What is a schematic? A schematic is a diagram that represents the elements of a system without using realistic pictures 2. Which of the following is a schematic? U3e-L3 Review March 04, 2010 DRILL 1. What does the following schematic symbol represent? DC Power Supply 2. What does the following schematic symbol represent? AC Power Supply 3. 4. How many volts are typical in a residential electrical outlet? 120 volts What do graphs of DC and AC power sources look like? Why? U3e-L8 Review Problems – Joule’s Law 1) Write the given information: V = 144 Volts P = 20,000 Watts I=? 2) Sketch a schematic diagram of the circuit: Start with power source Add conductors P = 20,000 W Add load Add current I=? + V = 144V U3e-L2 Review Problems – Joule’s Law 1) Write the given information: V = 144 Volts P = 20,000 Watts I=? 2) Sketch a schematic diagram of the circuit: + R=? - V = 5V I = .7A 3) Rearrange, Substitute, and Solve P=VxI I=P/V I = 20,000W / 144V R = 138.9 A U3e-L2 Review Resistance Calculations • Resistors in series are added: R1 R2 R3 Total Resistance: R T = R1 + R2 + R3 U3e-L3 Review Resistance Calculations • Resistors in parallel: add their reciprocals R1 R2 R3 Total Resistance: 1 1 1 1 = R T R1 + R2 + R3 U3e-L3 Review ELECTRIC MOTORS What is a schematic? A schematic is a diagram that represents the elements of a system without using realistic pictures. How would a schematic which includes an electric motor look? Switch = Commutator Motor V = 9V U3e-L8 I Review ELECTRIC MOTORS • Now that you know what switches look like in electrical schematics, draw an electrical schematic for a lamp plugged into a wall outlet. • Remember that AC power supplies look like in electrical schematics. U3e-L8 Review ELECTRIC MOTORS Lamp 120 V U3e-L8 Review TERMINOLOGY • Resistance (R) –a measure of the degree to which an object opposes an electric current through it . • Resisting an electric current often generates heat. – This is the principle behind how light bulbs work. • Resistance is measured in Ohms (W – the Greek letter Omega) U3e-L2 Review Electric Motors • Michael Faraday (1791-1867) – London, England. – Physicist and Chemist • First person to successfully create an electric motor. • Discovered that electric currents create a magnetic field, and vice versa. U3e-L8 Review ELECTRIC MOTORS • • Electric motors are used everyday in many ways. A motor’s purpose is to turn electrical energy into mechanical energy. Motors work on simple principles of magnetism: • Opposite poles _____________ ATTRACT • Like poles _____________ REPEL N S S S N N U3e-L8 Review Direct Current • If voltage is constantly 1.5 V, what does its graph over time look like? 2 1 Voltage (volts) 3 1.5 V 0 2 4 6 8 10 12 14 Time (seconds) U3e-L8 Review Alternating Current 0 120 +/-120 V -120 Voltage (volts) • If voltage is alternating 120 V to -120 V, what does its graph over time look like? 0 2 4 6 8 10 12 14 Time (seconds) U3e-L8 Review Electrical Technology • Electricity can be used in a thousand different ways. For example: – Electric motors turn electricity into motion. – Light bulbs, fluorescent lamps and LEDs turn electricity into light. – Computers turn electricity into information. – Telephones turn electricity into communication. – TVs turn electricity into moving pictures. – Speakers turn electricity into sound waves. – Stun guns turn electricity into pain. – Toasters, hair dryers and space heaters turn electricity into heat. – Radios turn electricity into electromagnetic waves that can travel millions of miles. – X-ray machines turn electricity into X-rays. U3e-L1 Review March 2, 2010 DRILL ELECTRICAL 1. An electric motor converts _________ energy into __________ MECHANICAL energy. 2. List 4 household objects that use electric motors. Fans ALMOST Refrigerators Pumps Garbage disposer EVERY MECHANICAL Printers Microwave trays MOVEMENT IN YOUR HOUSE Washing machines DVD players Vacuums VCRs U3e-L6 U3e-L6 U3e-L6 Review Problems – Joule’s Law Complete problem #5 on your worksheet U3e-L2 Review Problems – Joule’s Law 5. A Lexus RX 100h hybrid has a 144 Volt battery system in its trunk. The electric motor that the batteries power can generate 20,000 Watts of power. Sketch a schematic diagram of this circuit. What is the current traveling through this high voltage circuit? 1) Write the given information: 144 volts A schematicVis= a diagram that P = 20,000 watts represents the elements of a system I=? without using realistic pictures U3e-L2 ReviewProblems – Joule’s Law 1) Write the given information: V = 144 Volts P = 20,000 Watts I=? 2) Sketch a schematic diagram of the circuit: Start with power source Add conductors P = 20,000 W Add load Add current I=? + V = 144V U3e-L2 Review Problems – Joule’s Law 1) Write the given information: V = 144 Volts P = 20,000 Watts I=? 2) Sketch a schematic diagram of the circuit: + R=? - V = 5V I = .7A 3) Rearrange, Substitute, and Solve P=VxI I=P/V I = 20,000W / 144V R = 138.9 A U3e-L2 • STUDY FOR TEST TOMORROW • HAND IN REVIEW BEFORE TEST U3e-L2