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What is electricity? • Electricity is the flow (movement) of electrons! Conductor vs. Insulator • Conductors are materials that allow an electric current to pass. – Metals • Insulators are materials that do not allow an electric current to pass – Nonmetals, plastic, glass, wood, rubber Two Main Types of Electricity • Static Electricity – Electric charges (electrons) that buildup and collect on an object Static Electricity • When you rub two objects together…a balloon and your hair…electrons are transferred from one object to the other Van de Graaff Generator AC vs DC Current • Direct Current – The electrons flow steadily in a single direction • Alternating Current - The electrons keep switching directions, sometimes going “forwards” and then going “backwards” • Any movement of electrons is a current! • AC vs DC Current Video AC/DC • The band AC/DC chose the name to symbolize the bands “raw energy” when performing How is an Electric Current Generated? • Scientists found that electrical and magnetic fields are related • A magnetic field near a wire causes electrons to flow in a single direction along the wire – This is because the electrons are repelled and attracted by the north and south poles – Electric Current Generation Video DC Electric Motor • An electric motor is simply a generator with a power source attached – This causes the wire to spin because of the opposing charges provided by the battery Making Our Own Simple DC Motor The AC vs DC War • In the late 1800’s Thomas Edison promoted the use of DC current as a standard • During the first few years of electrical distribution DC current was the standard for the US Westinghouse Edison • George Westinghouse was a proponent of using AC current • Edison did not believe AC current would work efficiently (he also held all the patents for DC current use) The AC vs DC War • Advantages of DC – Was easy to make DC run at a voltage that could be widely used (100 volts) – DC motors were common (AC motors were not) – Could be used with batteries easily (Chemical batteries provide DC power) • Disadvantages of DC – Generating plants (or substations) were required within one mile of the load (homes) • This is due to the high resistance nature of running low voltage The AC vs DC War • Advantages of AC – Could be transmitted at very high voltages (100,000 or more) • This allowed it to be transmitted much further without as many substations (100’s of miles) • Disadvantages of AC – AC motors were rare, and expensive – To charge a battery a power inverter is required (converts AC DC) Michael Faraday • In 1831 Faraday discovered electromagnetic induction – He discovered that a changing magnetic field is necessary to induce a current in a nearby wire (circuit) • This is the basis of an electrical generator Voltage, Current, Resistance • What’s the difference?! Abbreviation Measured in Voltage V (or E) Volts (v) Current I Amperes (amps) Resistance r Ohms (Ω) Voltage • Voltage is defined as the “potential difference” from one point on a circuit to another – Think of voltage as the water pressure in a hose • A voltage can be measured even when no electrons are moving between the points as it is a measure of potential energy that will not be released until the electrons begin to flow. – Even if water valve is closed, there is still pressure (voltage) Current • Current is the rate of flow of electrons – This is like the amount of water flowing through a pipe • One amp = 1 coulomb per second – One coulomb = = 6.242 × 1018 electrons – 6,242,000,000,000,000,000 electrons per sec. Resistance • Resistance is the opposition to the passage of a steady electric current Two things can affect resistance: thickness of the wire, and the material the wire is made out of Ohms Law!!! I = V/R To make a current flow through a resistance there must be a voltage across that resistance What is the current that flows through a circuit that is supplied with 120 volts and has a resistance of 52 ohms? What are electric circuits? Circuits typically contain a voltage source, a wire conductor, and one or more devices which use the electrical energy. What is a series circuit? A series circuit is one which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit will fail. What is a parallel circuit? A parallel circuit has multiple pathways for the current to flow. If the circuit is broken the current may pass through other pathways and other devices will continue to work. Resistance in Series vs. Parallel Circuits • Resistance is higher in series circuits because the electrons only have one path to follow • Rtotal = R1 + R2 + Rn • Resistance is lower in parallel circuits because the electrons can flow along many paths Power Source • Provides a specified voltage to provide current to your circuit Resistors • Decrease current flow in a circuit • Dissipate power (usually in the form of heat) Capacitors • Capacitors store energy • This allows many things – Can be used to supply power even when power if off (for a short time) – Can “buffer” power supply when high current draw LED’s • Light Emitting Diodes – Special type of diode that emits light – Very low power consumption – Come in all sorts of colors Transistors • Transistors allow a small current (mA’s) to trigger a larger current flow • Small current goes into the base and allows larger current to flow through the collector and emitter Sort of like a switch Integrated Chips (IC’s) • Chips contain tens, hundreds, or even thousands of components inside them • For example a 555 Timer contains: – 20 transistors – 2 diodes – 16 resistors