Chapter+34+and+35

​**Key Definitions** **: **
 * 1) Diode - an electronic device that resists current to flow in a single direction in an electric circuit.
 * 2) Ampere - A unit of electric current in a meter-kilogram-second system. It is the steady current that when flowing in straight parallel wires of infinite length and negligible cross section, separated by a distance of one meter in free space, produces a force between the wires of 2 × 10 -7 newtons per meter of length.
 * 3) Direct current - An electric current flowing in one direction only.
 * 4) Alternating current - An electric current that reverses direction in a circuit at regular intervals.
 * 5) Resistor - A device used to control current in an electric circuit by providing resistance. (noun)
 * 6) Resistance - the tendency for a material to oppose the flow of electrons, measured in Ohms.
 * 7) Ohms law - the relationship between the three measurable quantities of electric circuits : Voltage, Resistance, and Amperage

**Notes:**


 * Chapter 34**

Electric current is the flow of electric charge that occurs when there is a potential difference across the ends of an electric conductor.
 * Electrical Flow continues until both ends reach a common potential.
 * Dry cells, wet cells, and electric generators are voltage sources that maintain a potential difference in a circuit.

The amount of current that flows in a circuit depends on the voltage and the electric resistance that the conductor offers to the flow of charge.
 * An increased temperature or a longer wire increases resistance.
 * A thicker wire decreases resistance.

Ohm's law states that the amount of current is directly proportional to the voltage and inversely proportional to the resistance.
 * Resistors are used in many electric devices to control current.
 * Electric shock is the result of electric current passing through the body when there is a voltage difference between two parts of the body.

Direct current (dc) is electric current in which the charge flows in one direction only; electrons in alternating current (ac) alternate their direction of flow.
 * Batteries produce direct current. Power utilities produce alternating current.
 * Alternating current allows low-cost, high-voltage energy transmission across great distances, with safe low-voltage use by the consumer.

Electric fields travel through circuits at nearly the speed of light, but the electrons themselves do not.
 * In a dc circuit, electrons have a low drift speed within wires.
 * In ac circuits, energy, not electrons, flows from the outlet; the electrons superimpose a rhythmic vibration on rapid random motion.

Electric power, the rate at which electric energy is converted into other forms of energy, is equal to the product of current and voltage.

Series Circuit
 * In a series circuit, all components are connected end to end, forming a single path for electrons to flow.
 * A major disadvantage for this pathway circuit is that if one area of connection fails, all along the pathway fail.
 * The lights on a Christmas tree are connected on a series circuit.

Parallel Circuit
 * In a parallel circuit, all components are connected across each other, forming exactly two sets of electrically common points.
 * As the number of parallel branches is increased, the overall resistance of the circuit is decreased.
 * The overall resistance is lowered with each added pathway between two points of the circuit.


 * Chapter 35**

Any path along which electric charge (usually electrons) can flow is a circuit.
 * A complete circuit is needed to maintain a continuous flow of charge.

In a series circuit, electrical devices form a single pathway for electron flow.
 * A break anywhere in the path stops the electron flow in the entire circuit.
 * The total resistance is equal to the sum of individual resistances along the current path.
 * The current is equal to the voltage divided by the total resistance.
 * The voltage drop across each device is proportional to its resistance.
 * the sum of voltage drops across the resistance of each individual device is equal to the total voltage.

In a parallel circuit, electrical devices form branches, each of which provides a separate path for the flow of electrons.
 * Each device connects the same two points of the circuit; the voltage is the same across each device.
 * The amount of current in each branch is inversely proportional to the resistance of the branch.
 * The total current is equal to the sum of the currents in each branch.

Electric circuits are often described by schematic diagrams, in which each element of the circuit is represented by a symbol.

In a circuit with several resistors, the equivalent resistance is the value of the single resistor that would comprise the same load to the battery or power source.
 * For resistors in series, the equivalent resistance is the sum of their values.
 * For resistors in parallel, the equivalent resistance is less than the value of any individual resistor.

Lines carrying an unsafe amount of current are overloaded.
 * To prevent overloading, fuses or circuit breakers are inserted in lines that provide power. Excessive current will "blow out" the fuse or "trip" the circuit breaker, stopping the current.
 * A short circuit is often caused by faulty wire insulation.

**Pictures:**




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Links: ** [|Interactive Guide to Circuits] [|Guide To Current]

[|Extra Practice]
1. Ture or False: Birds stand on telephone wire without being electrocutedbecause they are not grounded, so the current does not pass through them because they are not the path of least resistance.
 * Test Questions: **

2. Resistance in a circuit is generally measured in units of. A. Ohms B. Volts C. Amps D. Seconds

3.Which of the following is the correct expression of Ohm's Law? A. R= P/V B. I= P/V C. I = V/R

4. Voltage is abbreviated "V," and is measured in __blank__ or __blank__. A. Volts or Amps B. Joules or Amps/Hour C. Volts or Joules/Coulomb D. Volts or Meters/Second

5. True or False: In a series circuit of Christmas lights, if one bulb bulb burns out, all the bulbs go out.

6. True or False: Here in the United states we receive our electricity through direct currents.

7. What is the minimum current fatal to humans? A. 0.001 B. 0.005 C. 0.010 D. 0.070

8. True or False: Electrical current always travels in a straight path.

9. True or False: In a parellel circuit, if one bulb fails, the whole circuit fails.

10. True or False: An increase in temperature or a longer length of wire will increase resistance.

**Record the answers to the above questions at the link below** Answers to Test Questions