Download Electricity

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
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.
 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.
-
+
 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.
 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.
- - - - - - - - - - - - -
 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.
 Electric
Current always flows from higher
voltage to lower voltage, but electrons in a
circuit actually flow from lower voltage to
higher voltage.
 Diagram:
 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
 What
A
exactly is a battery??
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
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.
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
 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.
https://www.youtube.com/watch?v=ian6NyXpszw
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
 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.
 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.
 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.
 The
main switch and circuit breaker or
fuse box serve as an electrical
headquarters for your home.
 Parallel
circuits branch out from the
breaker or fuse box to wall sockets, major
appliances, and lights.
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.
 To
protect against overheating of the
wires, all household circuits contain
either a fuse or a circuit breaker.
 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.
 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.
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.
 https://www.youtube.com/watch?v=zYS9kdS
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