Circuit A circuit is a path for electrons to flow through. The path is from a power sources negative terminal, through the various components and on to the positive terminal. Think of it as a circle. The paths may split off here and there but they always form a line from the negative to positive. NOTE: Negatively charged electrons in a conductor are attracted to the positive side of the power source. Simple Circuit If we break a circuit down to it's elementary blocks we get: 1) A Power Source -- eg: battery 2) A Path -- eg: a wire 3) A Load -- eg: a lamp 4) A Control -- eg: switch (Optional) 5) An indicator -- eg: Meter (Optional) Series Circuit A series circuit is one with all the loads in a row. Like links in a chain. There is only ONE path for the electricity to flow. If this circuit was a string of light bulbs, and one blew out, the remaining bulbs would turn off. There are specific properties to this circuit that will be described in another section. NOTE: The squiggly lines in the diagram are the symbol for Resistors. The parallel lines are the symbol for a battery. Parallel Circuit A parallel circuit is one that has two or more paths for the electricity to flow. In other words, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out there is still current flowing to the others as they are still in a direct path from the negative to positive terminals of the battery. There are specific properties to a parallel circuit that will be described in another section. Combination Circuit A combination circuit is one that has a "combination" of series and parallel paths for the electricity to flow. Its properties are a synthesis of the two. In this example, the parallel section of the circuit is like a sub-circuit and actually is part of an over-all series circuit.
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Series andParallel Circuits
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Circuit Defined A circuit is a path for electrons to flow through. The path is from a power source’s negative terminal, through the various components and on to the positive terminal Types Series Parallel 2
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Components - SourceDRY CELL a source of electrical energy - + 3
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Components - Load LIGHT BULB lights up when electricity pass through 4
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Circuit - Complete Source of electrical energy AppliancesComplete circuit - + Electricity flows 5
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Terms to Know Open circuit – there is a break somewhere and electricity cannot flow (maybe the switch is open) Closed circuit – electricity can flow (the switch is closed) Short circuit – the electricity completes a circuit without going through the load Load – what is using the electricity 6
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SchematicsCircuit diagrams, also called schematic diagrams, provide a graphic representation of an electric circuit using standard symbols. 7
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Diagram Symbols wire or conductor resistor or other load bulb V voltmeter battery A ammeter switch generator 8
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Example – Simple Circuit - + circuit diagram A + - A 9
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Complex Circuit - + A Construct the circuit diagram + - A 10
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SeriesIfyou add a resistor (like another light): Total resistance goes UP since all the current has must go through each resistor.
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Adding Resistors toSeries: Current in the circuit will go DOWN (lights will dim) If you remove a light bulb or one burns out —all go out!
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Current in SeriesCurrent is the same at all pointsUse Ohm’s Law to find current using resistance and voltage
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Voltage in SeriesVoltage isreduced by eachresistance –voltage drop
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Resistance in SeriesAdd up all resistors toget total Totalresistance will go up because all of the current must go through each resistor.
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Sample Problem #1 Draw a series circuit with two 1.5 V batteries, 3 resistors, and a current of 0.5 A.1. What is the total voltage of the circuit?2. What is the resistance of each resistor?
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Parallel CircuitsHas at least one point where current dividesMore than one path for current to flowPaths are also known as branches
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Parallel:Ifyou add a resistor: Total resistance goes down Total current goes up when you add another path
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Removing a LightBulbIf you remove a light bulb or one burns out, the others stay on because the circuit is still closed.
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Current in ParallelCurrent flows into a branching point, the same total current must flow out againCurrent depends on resistance in each branch
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Voltage in ParallelVoltageis thesame across eachbranch – becauseeach branch is onthe same wire
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Resistance inParallelCalculate current in each branch based on resistance in each branch by using Ohm’s Law
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Practice problem #2 Draw a parallel circuit with two resistors (one on each branch) and a 12 V battery.1. What is the voltage through each resistor?
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Toll BoothExplanation Adding toll booths in series increases resistance and slows the current flow. Adding toll booths in parallel lowers resistance and increases the current flow.
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In series—The voltage is increased.In parallel—No change in voltage; these batteries will last longer!
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One More FINAL Thing:Two Types of Current:DC—Direct Current— produced by solar cells and chemical cells (batteries)Current only flows in one direction.
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2 type of current: ndAC—Alternating CurrentCurrent flows back and forth (alternates)Found in homesGenerators produce AC current
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