Transcript PPTX format

Power
a.k.a. Electricity
What is electricity?
Electrons in Atoms
 All matter is made up of
atoms.
 Atoms are comprised of:
protons
neutrons
electrons
 Electrons circle the space
outside the nucleus
How electrons create a charge
 Electrons carry a negative charge.
 Electrons can move from one atom to another.
 The material that picks up an electron is negatively charged.
 The material that loses an electron is positively charged.
Opposites attract
 Objects with a net positive
charge will be attracted to
objects with a negative
charge.
 Two objects with the same
charge will repel each
other.
Static Electricity Experiment
 Friction causes electrons to
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move from one object to
another.
Rub a balloon against the
carpet.
The balloon will pick up
extra electrons and will be
negatively charged.
Touch the balloon to the
wall. The wall is neutral.
What happens?
Experiment with light bulb
 Experiment with comb and light bulb
 Can we generate enough of a charge to cause a light bulb to
light up?
Electricity in motion
 Different from static electricity
 Electrons moving from one atom to the next.
 Called a current.
Demonstration of current
 This is a closed circuit.
Demonstration of current
 The switch allows the circuit to be open and closed.
Lights in series
 Lights are connected in a
continuous circle.
 If one bulb goes out – the
circuit is broken and none
work.
 All bulbs must share the
current. The more bulbs
on the string, the dimmer
the light becomes.
Lights in parallel
 Each light gets the full
amount of current.
 If one bulb goes out –
others will still work.
 All electricity in home is
wired in parallel.
Historical Figures in Electricity
William Gilbert (1544-1603)
 First person to use
the term “electric”
 Invented a device
called the
“vensorium” if it
moved toward an
object then Gilbert
called the object
electric.
Benjamin Franklin (1706-1790)
 First to discover the principle of
“conservation of charge” - an accounting
relationship between the amount of charge
in a region and the flow of charge into and
out of that region
 Wanted to verify that lightning was a form
of electricity and flew a kite in a storm. The
idea was to get lightning to strike the kite
and have the charge run down the string to
the key attached to the end of it.
Charles Coulomb (1746-1806)
 Studied the amount of
attraction/repulsion
between charged objects.
 Coulomb’s law: the force
between two charges is
inversely proportional to
the square of the distance
between them.
Allessandro Volta (1745-1827)
 Invented the voltaic pile (battery).
 Volta stacked several pairs of alternating
copper and zinc disc separated by cloth.
When the top and bottom contacts were
connected by a wire, an electric current
flowed through the voltaic pile and the
connecting wire.
 The strength of the battery is given in
volts.
Georg Ohm (1789-1854)
 Discovered the concept of
resistance.
 Ohm’s law states that there is a
direct proportionality between
the potential difference (voltage)
applied across a conductor and
the resultant electric current.
 V=I*R
Michael Faraday (1791-1867)
 Discovered electromagnetic
induction which is the the
generation of an electric current by
passing a metal wire through a
magnetic field.
 Principle behind the operation of
generators, transformers, etc…
James Wimshurst (1832-1903)
 Invented a device (the Wimshurst
machine) that could deliver an electric
charge.
 Predecessor to the modern generator
– a device that converts mechanical
energy to electrical energy.
Thomas Edison (1847-1931)
 Invented the light bulb
 Worked on selling the concept of
bringing electricity into the home.
 Edison patented a system for
electricity distribution in 1880
(essential for capitalizing on the
invention of the electric lamp) and
established Edison Illuminating
Company providing 110 Volts of
DC current to 59 customers in
Manhattan.
 Advocated against AC.
Nikola Tesla (1856 – 1943)
 Rival of Thomas Edison
 Developing the modern alternating
current (AC) electrical supply system
 Worked for Edison’s company but left
after being treated badly.
 In 1885, Westinghouse corporation
bought the patent rights to Tesla’s
system of dynamos, transformer and
motors and used Tesla’s alternating
current system to light the World’s
Columbian Exposition of 1893 in
Chicago.
Working with electricity
Measuring Electricity
VOLTS (E)
 measure the “pressure” under which electricity flows.
AMPS (I)
 measure the amount of electric current.
WATTS (P)
 measure the amount of work done by a certain amount of current
at a certain pressure or voltage.
P = E * I (1 watt = 1 volt * 1 amp)
Measuring Electricity
VOLTS (E)
 measure the “pressure” under which electricity flows.
AMPS (I)
 measure the amount of electric current.
WATTS (P)
 measure the amount of work done by a certain amount of current
at a certain pressure or voltage.
P = E * I (1 watt = 1 volt * 1 amp)
Measuring Electricity
Make some calculations
 Power (watts) = Voltage (volts) * Current (amps)
 E.g. A current of 2 Amps flowing through a bulb with 12
Volts across it generates 24 watts of power.
 Take the quiz: http://rikravado.hubpages.com/hub/Wattare-Amps-and-Volts
Power: USA vs. UK
USA
UK
 In the USA, the domestic
 In the UK, domestic power
supply is typically 110V
(safer than the UK) and
this means a 100W bulb
draws a current of
100/110 Amps (about
0.9A).
is supplied at 240 Volts. A
100 Watt bulb will
therefore draw a current of
100/240 Amps (about
0.4A).
What do fuses do?
 A fuse is used in a circuit to protect
the other elements in a circuit.
 Fuses are rated at different currents
and voltages. When the rated
current is exceeded the fuse will
blow.
 For example you find fuses in your
home. If there was a sudden surge
in current coming into your house
the fuse will blow and power will
be cut to the circuit it is attached
to. If that fuse wasn't there the
other elements in that circuit would
be exposed to the current surge.
This would cause damage to that
object
 Patented by Thomas Edison.
Conductors vs. insulators
 A good conductor is a material where each atom has one
or more free electrons.
 These become mobile free electrons that create a charge.
 Good Conductors
 Good Insulators
 Copper
 Wood
 Silver
 Fibrous materials
 Graphite
 Chalk
 Charcoal
 Hair
 Watery Materials
 Feathers
 Dried Vegetables
What is resistance?
Not all conductors are equal
 Some metals allow electrons to move more freely than others
– we call them less resistant than others.
 Copper has low resistance, silver is slightly higher.
 The longer the wire – the more the resistance.
 The discovery of resistance was quantified by Georg Ohm
who stated:
 V = I * R – where R is resistance
What are resistors?
 Resistors are included in a
circuit to add resistance.
 Using Ohm’s law, you can
figure out what type of
resistance to use to achieve a
certain current with a given
amount of voltage.
 Practice making calculations:
 http://www.sengpielaudio.c
om/calculator-ohm.htm
How to we manufacture and
manage electricity?
What is AC (alternating current)?
 Power supplied to homes and
buildings is AC current.
 Alternating Current (AC) flows
one way, then the other way,
continually reversing direction.
 An AC voltage is continually
changing between positive (+)
and negative (-).The rate of
changing direction is called the
frequency of the AC and it is
measured in hertz (Hz) which is
the number of forwardsbackwards cycles per second.
Advantages of AC current
 Travels farther without losing energy and can transfer
different amounts of power.
 AC voltage from a generator in a power plant can be bumped
up or down in strength by another mechanism, called a
transformer.
How do you make AC?
 If a machine is constructed to
rotate a magnetic field around
a set of stationary wire coils
with the turning of a shaft,
AC voltage will be produced
across the wire coils as that
shaft is rotated, in accordance
with Faraday's Law of
electromagnetic induction.
This is the basic operating
principle of an AC generator,
also known as an alternator:
How do AC appliances work?
 AC appliances don’t care
that the electrons are not
moving continually in one
directions – just that
electrons are moving at all.
How is electricity generated at a power
plant?
 Some fuel source, such as coal,
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oil, natural gas, or nuclear
energy produces heat.
The heat is used to boil water to
create steam.
The steam under high pressure
is used to spin a turbine.
The spinning turbine interacts
with a system of magnets to
produce electricity.
The electricity is transmitted as
moving electrons through a
series of wires to homes and
business.
What is a transformer?
 Transformers are used wherever an electrical voltage needs to
be increased or decreased.
 They are commonly seen on electrical poles.
 Power plants produce electricity at a very high voltage so that it
can travel great distances. The voltage must be reduced,
however, before the electricity reaches homes and other
buildings that use it to power appliances, machinery and other
devices.
How does electricity get to your home?
 Electricity is made at a power plant by huge
generators. Most power plants use coal, but
some use natural gas, water or even wind.
 The current is sent through transformers to increase
the voltage to push the power long distances.
 The electrical charge goes through high-voltage
transmission lines that stretch across the
country.
 It reaches a substation, where the voltage is
lowered so it can be sent on smaller power line
How does electricity get to your home?
 It travels through distribution lines to your
neighborhood, where smaller pole-top
transformers reduce the voltage again to take the
power safe to use in our homes.
 It connects to your house through the service drop and
passes through a meter that measures how much
our family uses.
 The electricity goes to the service panel in your
basement or garage, where breakers or fuses
protect the wires inside your house from being
overloaded.
 The electricity travels through wires inside the walls to
the outlets and switches all over your house.
Discussion / Research
Questions to investigate
 Where is most of the electricity generated for the St. Louis
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population?
How much electricity does the typical American use?
How does electricity usage in the US differ from usage in
other countries?
Is it possible to convert AC to DC power or vice versa?
Where is DC power used? Why is it appropriate in these
settings?