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Electrical Theory Electrical Theory • Electrical Theory – Atoms have a center called a nucleus or center made of protons (positive particles) and neutrons (neutral particles) – Electrons (negative particles) orbit the nucleus – And atom may have one of or more electrons orbiting the atom and at different distances from the nucleus – Electrons have the ability to travel, leave one atom and go to another Electrical Theory • Electrical Theory – In some matter, electrons are bound tightly together and can leave only with great difficulty – In other matter the bond is so relaxed that electron move easily – Matter or materials whose electrons can travel easily are called conductors – Matter that prohibits the free movement of electrons to travel are called insulators. – Metals conduct electricity because they have a great number of free electrons. Electrical Theory • Electrical Theory – If a negative charged body is connected to a positive charged body by a conductor, the electrons will be attracted to the positive particles. – Nature prefers everything to be neutral. – This flow of electrons is called a current. – Equilibrium is a term used to describe when a balance has been reached. Electrical Theory • Electrical Theory – The difference in concentrations of these electrons in matter is known as different potentials. – Electrical potential is the ability to provide free electrons. – In electricity the difference in potential is measured in volts. Electrical Theory • Electrical Theory – There are two types of currents, Direct current (dc) and alternating current (ac). – Direct current flows in one direction only. – Alternating current changes it’s flow (in reverse) 60 times each second, known as 60 hertz or 60 cycles. – A cycle is one complete electrical wave or vibration. Electrical Theory • Electrical Theory – To maintain a flow of electron it is necessary to have a source which is always at a greater electrical potential. – Meaning to always have an excess of free electrons. – That energy can be produced chemically (battery) or mechanically (generator). Electrical Theory • Electrical Theory – Battery (voltaic cell) • Copper and zinc rods • Acid solution • Acid strips electrons from the copper rod • Electrons travel to the zinc rod • Resulting in the copper rod having less electrons and becoming the positive pole (anode). • The zinc rod having an excess of electrons and becoming the negative pole (cathode). Electrical Theory • Electrical Theory – Battery (voltaic cell) • A group of cells is called a battery • Circuit is produced when there is a conductor and a load placed on the positive and negative ends of the battery. – Dry cell or wet cell • Dry cell use a chemical paste (acid paste) – Used in remotes, walkmans, & cameras • Wet cell uses a liquid chemical (acid) – Used in your car Electrical Theory • Electrical Theory – No electron flow without a pathway – The pathway is known as a circuit. – A simple circuit needs: • • • • A power source. Conductors. A load or loads. A device for controlling current. Electrical Theory Electrical Theory • What happened when a pathway was place from the battery to the load and back to the battery? • Remove the conductor from the positive post. What happens? • Open and Closed circuit. • In Theory explain what is happening inside the battery and what happens when the circuit is closed. Electrical Theory Electrical Theory • What purpose does the switch serve? • Relate an electrical switch to a water supply system. • I this a series or a parallel circuit? • Where is the load? • What happen if there is no load? The connection is made from pole to pole with no energy being used? Electrical Theory Electrical Theory • What is different? • Why? • In a series circuit the resistance on one device affects the rest of the loads on the circuit. • How can this affect can this have on equipment or appliances? • Wire the three loads using a parallel circuit. Electrical Theory Electrical Theory • What is different? • Why? • Which type of circuits do think is generally used in homes? • Place a device to open and close each lamp/load on the circuit. Electrical Theory Electrical Theory • How does this circuit differ from the from the previous series circuit? • What are the advantages of a parallel circuit? Electrical Theory Ohm’s Law Current in a circuit is directly proportional to the voltage applied to the circuit and is inversely proportional to the resistance of the circuit Electrical Theory The rate of the flow of the current is equal to electromotive force divided by resistance • I = Intensity of Current = Amperes • E = Electromotive Force + Volts • R = Resistance = Ohms • P = Power =Watts • The Three Basic Ohm’s Law Formulas are: I= E R R= E I E=IxR Electrical Theory E I R Electrical Theory P Power (Watts) W Resistance (OHMS) Ω R I Current (Amps) A Voltage (Volts) V E Electrical Theory Electrical Theory Ohm’s Law An electric appliance is rated at 1200 Watts, and connects to a 120 Volt outlet. How much will it draw? (amps) Amperes = Watts Volts I= P E I= 1200 120 = 10A What is the Resistance of the same appliance? Ohm’s = Volts Amperes R= E I R= 120 10 = 12 Ω Electrical Theory Ohm’s Law Series Circuits In the example, we know the following values: I = amps = 10 R = ohms = 12Ω E = volts = 120 P = watts = 1200 Electrical Theory Ohm’s Law Series Circuits • What is given? – Ohms • 1Ω + 2Ω + 3Ω = 6Ω – Volts • Given 6volts – What value do we need? – Amperage (I) • 6volts ÷ 6Ω = 1 Amp Electrical Theory Ohm’s Law Series Circuits E = 6 volts • Calculate the watts from the same circuit. • What method can be used? – – – – P = E x I, I2R, E2 ÷R E x I = P, 6 x 1 = 6 watts I2R, 12 x 6 = 6 watts E2 ÷R, 62 ÷ 6 =6 watts R = 6 ohms I = 1 amp P = ?? 6 watts Electrical Theory