ch20_cfrn

**Chapter 20: Circuits and Circuit Elements**

20-1: Schematic Diagrams and Ciruits

Schematic Diagrams
 * **Schematic Diagrams**- A diagram that depicts the construction of an electrical apparatus.
 * **Electric Circuit**- A set of electrical components connnected so that they provide one or more ompete paths for the movement of charges.
 * **Load-** Any element or group of elements in a circuit that dissipates energy.
 * **Closed Circuit-** The path from one battery terminal to the other is complete, a potential difference exists, and electrons move from one terminal to the other. In other words, there is a closed-loop path for electrons to follow.
 * **Open Circuit**- Without a complete path, there is no charger flow and therefore no current. This situation is an open circuit.
 * Light bulbs contain a complete conducting path
 * Short circuits can be hazardous
 * The source of potential difference and electrical energy is the circuit's emf
 * **Emf-** The energy per unit charge supplied by a source of electric current.
 * For conventional current, the terminal voltage is less than the emf
 * Potential difference across a load equals the terminal voltage
 * When charges move conventionally in a battery, the potential difference across the battery's terminals, the **terminal voltage**, is actually slightly less than the emf.
 * Potential difference across a load equals the terminal voltage

Below is a chart of all of the symbols to use when making diagrams.



20-2 Resisors in series or in parallel

Resistors in Series
 * Resistors in series have the same current
 * When many resistors are connected in series, the current in each resistor is the same.
 * Thus, to find the total current, first use the individual resistance values to find the total resistance of the circuit, called **equivalent resistance**, then the equivalent resistance can be used to fine the current.
 * **Series-** describes a circuit or portion of a circuit that provides a single conducting path without junctions.
 * Resistors in series have the same current.
 * When many resistors are connected in series, the current in each resistor is the same.
 * The equivalent resistance in a series circuit is the sum of the circuit's resistance.
 * Resistors In Series:
 * R1+R2+R3...
 * Equivalent resistance equals the total of individual resistances in series.
 * The equivalent resistance of a series combination of resistors is always greater than any individual resistance.
 * Series circuits require all elements to conduct.

Resistors in Parallel >   > When resistors are wired in parallel with an emf source, the potential difference across each resistor always equals the potential difference across the source. > Additionally, the equivalent resistance of several parallel resistors is less than the resistance of any of the individual resistors. Thus, a low equivalent resistance can be created with a group of resistors of higher resistances. > > 20-3 Complex Resistor Combinations > > When determining the equivalent resistance for a complex circuit, you must simplify the circuit into groups of series and parallel resistors and then find the equivalent resistance for each group by using the rules for finding the equivalent resistance of series and parallel resistors. > > Work backward to find the current in and potential difference across a part of a circuit > There is no single formula for finding the current in and potential differnce across a resistor buried inside a complex circuit. 
 * **Parallel**- Describes two or more components in a circuit that are connected across common points or junctions, providing separate conducting paths for the current.
 * Resistors in parallel have the same potential differences across them.
 * The sum of currents in parallel resistors equals he total current.
 * Resistors In Parallel:
 *  1/Req=1/R1+1/R2+1/R3... 
 *   The equivalen resistance for a parallel arrangement of resistors must always be less than the smallest resistance in the group of resistors.
 * Parallel circuits do not require all elements to conduct


 * Practice Problems**:

1) A. 12.0 v storage battery is connected to three resistors, 6.75 Ω, 15.3 Ω, and 21.6 Ω, respectively. The resistors are joined in series. a. Calculate he rquivalent resistance. b. What is the current in the circuit?

2) A 7.0 Ω, resistor is connected in series with another resistor and a 4.5 V battery. The current in the circuit is 0.60 A. Calculate the value of the unknown resistance.

3) A 4.0 Ω resistor, an 8.0 Ω resistor, and a 12.0 Ω, resistor are connected in parallel across a 24.0 V battery. a. What is the equivalent resistance of the circuit? b. What is the current in each resistor?

Answers:

1) a. 43.6 Ω, b. 0.275 A

2) 0.5 Ω

3) a. 2.2 Ω, b. 6.0 A, 3.0 A, 2.00 A


 * __Holt, Rinehart and Holt Physics__. New York: Holt, Rinehart & Winston, 2001.**