# Electric Circuits. Danger – Do not attempt electrical work until you have learned the safe and proper technique from a certified electrician. Copyright.

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Electric Circuits

Danger – Do not attempt electrical work until you have learned the safe and proper technique from a certified electrician. Copyright © 2010 Ryan P. Murphy

 Electricity difference electrons negatively  Electricity is a force created by a difference in charges (+ & -) due to gained or lost electrons. (an electron is a negatively charged particle.) electrons moving electrical current.  When electricity is flowing between two points, this is actually electrons moving from point A to point B. This is called an electrical current.

difference in charges  In order for these electrons to flow, however, there must be a difference in charges (# of electrons built up) between the 2 points. (Just like heat flow needs a difference in temperatures.) negative positive  Electricity always flows from a location with a negative charge to a location with a positive charge. Like charges repel, opposites attract.  Remember: Like charges repel, opposites attract. - +

positive (+) negative (-) electrons flow from the bottom to the top  Think of a battery, the top has a positive (+) charge and the bottom has a negative (-) charge. So when they are connected, electrons flow from the bottom to the top.

difference in charges voltage  The difference in charges between 2 points is called the voltage. same no flow of electrons  2 points can both have a tremendous charge, but if the charge is the same then there will be no flow of electrons between them. - - - - - -

current  The number of electrons actually flowing through a conductor is called the current, and is measured in amperes (amps). 1 amp = 6.25 x 10 18 electrons per sec. (6,250,000,000,000,000,000!)

 So let’s say that using a voltmeter you determine that there are no electrons flowing from point A to point B through an extension cord connecting the two. Does that mean it is safe for you to touch either of the 2 points? Hmmm……

 No! There may be no electrons flowing because the charges are the same. However, your charge may be much different, which would allow the electricity to flow into you.

 Electric Currenthigher voltage to lower voltageelectrons lower voltage to higher voltage  Electric Current always flows from higher voltage to lower voltage, but electrons in a circuit actually flow from lower voltage to higher voltage.  Diagram:

resistors slow flow of electricity  Materials called resistors can slow the flow of electricity, without stopping it all together. conductorssmall resistance  Almost all materials, even good conductors, provide at least a small amount of resistance to an electric current. ohms  Resistance is measured in ohms. 

 What exactly is a battery?? direct currentchemical reaction  A battery is a device which produces a continual direct current, through a chemical reaction.

 Batteries can be composed of a liquid electrolyte (a liquid which will conduct an electric current) (wet cell) or a paste electrolyte (dry cell). Whether liquid or paste, the electrolytes are usually acidic.  Car and boat batteries are examples of wet cells, flashlight batteries are examples of dry cells.

electrons terminals  A chemical reaction inside the battery pulls electrons away from 1 of the terminals and gives them to the other. negative (-) positive (+)  This causes 1 terminal to be negative (-) and the other to be positive (+). connected flow of electrons from negative to positive  When these terminals are connected through a device, they produce a flow of electrons from negative to positive, which power the device.

 This will be you at some point in your life so pay attention.

 When you jump a car’s battery, ground the negative.  Avoid touching the cables together and notice the sequence, 1, 2, 3, 4. Copyright © 2010 Ryan P. Murphy

 When you jump a car’s battery, ground the negative.  Avoid touching the cables together and notice the sequence, 1, 2, 3, 4. Copyright © 2010 Ryan P. Murphy

 When you jump a car’s battery, ground the negative.  Avoid touching the cables together and notice the sequence, 1, 2, 3, 4. Copyright © 2010 Ryan P. Murphy

 When you jump a car’s battery, ground the negative.  Avoid touching the cables together and notice the sequence, 1, 2, 3, 4. Copyright © 2010 Ryan P. Murphy

 When you jump a car’s battery, ground the negative.  Avoid touching the cables together and notice the sequence, 1, 2, 3, 4. Copyright © 2010 Ryan P. Murphy

 Video! How to jumpstart a car. (Saab Ad?)  You will be driving soon, and may have to do this on your own. Is this an ad?  http://www.youtube.com/watch?v=li1PL6EpFF8 http://www.youtube.com/watch?v=li1PL6EpFF8

circuit  A circuit is a pathway along which an electric current can travel, en route to a device.  Locating a device along that pathway will allow it to be powered by the electric current. series parallel  There are 2 different types of circuits: series and parallel.

1 pathway for electricity to flow stop the flow of electricity  A series circuit is one which has only 1 pathway for electricity to flow. All devices are located along this single pathway, and any break in the circuit will stop the flow of electricity. old type Christmas tree lights & flashlights  Examples: old type Christmas tree lights & flashlights

 How can one faulty bulb cause a whole string of lights to go out? no current flows through the circuit  When any part of a series circuit is disconnected, no current flows through the circuit. open circuit  This is called an open circuit. The burned-out bulb causes an open circuit in the string of lights.

multiple paths which the electricity can travel down  A parallel circuit has multiple paths which the electricity can travel down, with different devices along the different paths. open or broken still carry electricity  If one pathways is open or broken, the others can still carry electricity. newer Christmas tree lights, household circuits Example: newer Christmas tree lights, household circuits

current continues to flow  When one branch of the circuit is opened, such as when you turn a light off, the current continues to flow through the other branches.

120 V  In the United States, the voltage difference in most branches is 120 V. 240 V  Some branches used for electric stoves or clothes dryers have a voltage difference of 240 V.

 The wiring in a house must allow for the individual use of various appliances and fixtures. parallel circuits  This wiring is mostly a combination of parallel circuits connected in an organized and logical network.

main switch circuit breaker fuse box  The main switch and circuit breaker or fuse box serve as an electrical headquarters for your home.

wall socketsmajor applianceslights  Parallel circuits branch out from the breaker or fuse box to wall sockets, major appliances, and lights.

short circuit current  A short circuit occurs when the current stops short of the intended device, usually because of the circuit being completed prior to reaching the device.

fuse circuit breaker  To protect against overheating of the wires, all household circuits contain either a fuse or a circuit breaker.

small piece of metalmeltscurrent becomes too high  An electrical fuse contains a small piece of metal that melts if the current becomes too high. break in the circuitflow of current  When it melts, it causes a break in the circuit, stopping the flow of current.

replace the blown fuse with a new one  To enable current to flow again in the circuit, you must replace the blown fuse with a new one.  Too many appliances in use at the same time  Too many appliances in use at the same time is the most likely cause for the overheating of the circuit.

 A circuit breaker is another device that prevents a circuit from overheating and causing a fire. switchautomatically flippedcurrent becomes too great  In a circuit breaker, a switch is automatically flipped when the current becomes too great.  Flippingcircuit current  Flipping the switch opens the circuit and stops the current. pushing switchon  Circuit breakers can be reset by pushing the switch back to its “on” position.