13g_resistors_series_parallel - Lesson 13g: Resistors in...

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Lesson 13g: Resistors in Series and Parallel Circuits Any path along which electrons can flow is a circuit. For a continuous flow of electrons, there must be a complete circuit with no gaps. A A gap is usually an switch that can be closed to allow electron flow or open to stop electron flow. If I wanted to draw a schematic diagram (aka circuit diagram ) of a resistor powered by a battery that can be turned off and on, it might look like Illustration 1. Note that the placement of the switch (SW1) near the positive terminal (what we would consider the end of the electron flow path) does not matter. A switch anywhere in the circuit will have the same effect of stopping current flow. Switches are shown in the open (off) position so they are easier to spot in the diagram. In a closed (on) position, the current would be able to flow through the whole circuit. Most circuits used in modern devices will have several components, hooked up in a variety of combinations. All of these circuits can be broken into two main categories, series and parallel . In all circuits, going through a battery increases voltage, while going across a resistor decreases voltage (a voltage “drop”). As you go around any single pathway the total voltage drops across all resistors must equal the voltage from the battery. Series Circuits In a series circuit there is only a single pathway for electron flow between the terminals of the battery. If you can trace only one pathway with your finger, it's a series circuit . When the switch is closed, a current exists almost immediately in all three resistors. The current does not “pile up” at any of the resistors, nor does it go at different rates in different parts of the circuit. If you are in line to get into a movie, it doesn't matter where you are standing; the whole line moves at the same speed. Everyone is affected by trying to get by the ticket window. For this reason we can say that the current is constant everywhere in a series circuit . 11/13/2010 © studyphysics.ca Page 1 of 10 Illustration 1: A simple schematic diagram of a battery connected to a switch and resistor. 9 V Illustration 2: A series circuit with three resistors.
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A break anywhere in the path results in an open circuit, and the flow of electrons stops. Burning out one resistor or simply opening a switch could cause such a break. The current has to flow through all these resistors, so overall we increase the resistance of a circuit when we place resistors in parallel. As mentioned earlier the total drops in voltage must equal the voltage from my battery along a single path (exactly what a series circuit is). Since V = IR we can say. .. V
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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13g_resistors_series_parallel - Lesson 13g: Resistors in...

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