electric circuits. danger – do not attempt electrical work until you have learned the safe and...

UNIT 6 SECTION 3

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 Electricity is a force created by a

difference in charges (+ & -) due to gained or lost electrons. (an electron is a negatively charged particle.)

When electricity is flowing between two points, this is actually electrons moving from point A to point B. This is called an electrical current.

ELECTRICITY 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.)

Electricity always flows from a location with a negative charge to a location with a positive charge. Remember: Like charges repel, opposites

attract.

- +

ELECTRICITY 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.

VOLTAGE (POTENTIAL DIFFERENCE) The difference in charges between 2

points is called the voltage.

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.

- - - - - - - - - - - - - - - - - -

ELECTRIC 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 1018 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.

CURRENT AND ELECTRON FLOW 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 Materials called resistors can slow the

flow of electricity, without stopping it all together.

Almost all materials, even good conductors, provide at least a small amount of resistance to an electric current.

Resistance is measured in ohms.

W

BATTERIES What exactly is a battery??

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.

A chemical reaction inside the battery pulls electrons away from 1 of the terminals and gives them to the other.This causes 1 terminal to be negative

(-) and the other to be 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.

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

ELECTRIC CIRCUITS 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.

There are 2 different types of circuits: series and parallel.

SERIES CIRCUIT 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.

Examples: old type Christmas tree lights & flashlights

SERIES CIRCUIT How can one faulty bulb cause a

whole string of lights to go out?When any part of a series circuit is

disconnected, no current flows through the circuit.

This is called an open circuit. The burned-out bulb causes an open circuit in the string of lights.

DIAGRAM OF SERIES CIRCUIT

https://www.youtube.com/watch?v=ian6NyXpszw

PARALLEL CIRCUITS A parallel circuit has multiple paths

which the electricity can travel down, with different devices along the different paths.

If one pathways is open or broken, the others can still carry electricity.Example: newer Christmas tree lights, household circuits

DIAGRAM OF PARALLEL CIRCUIT

ADVANTAGE OF PARALLEL CIRCUITS 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.

HOUSEHOLD CIRCUITS In the United States, the

voltage difference in most branches is 120 V.

Some branches used for electric stoves or clothes dryers have a voltage difference of 240 V.

HOUSEHOLD CIRCUITS The wiring in a house must allow for

the individual use of various appliances and fixtures.

This wiring is mostly a combination of parallel circuits connected in an organized and logical network.

HOUSEHOLD CIRCUITS The main switch and circuit breaker

or fuse box serve as an electrical headquarters for your home.

HOUSEHOLD CIRCUITS Parallel circuits branch out from the

breaker or fuse box to wall sockets, major appliances, and lights.

HOUSEHOLD CIRCUITS 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.

HOUSEHOLD CIRCUITS To protect against overheating of the

wires, all household circuits contain either a fuse or a circuit breaker.

FUSES An electrical fuse contains a small piece

of metal that melts if the current becomes too high.

When it melts, it causes a break in the circuit, stopping the flow of current.

FUSES 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 is the most likely cause for the overheating of the circuit.

CIRCUIT BREAKERS A circuit breaker is another device that

prevents a circuit from overheating and causing a fire.

In a circuit breaker, a switch is automatically flipped when the current becomes too great.

Flipping the switch opens the circuit and stops the current.

Circuit breakers can be reset by pushing the switch back to its “on” position.

CIRCUIT BREAKERS

VOLTS, OHMS AND AMPS https://

www.youtube.com/watch?v=zYS9kdS56l8