Electricity

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Transcript Electricity

Science 9 Unit D
Electrical Principles
and Technologies
^What is electricity?^
• ^Electricity comes from the Greek word
electron, which means amber.^
• Amber was used by a philospher Thales, to cause an
attraction to materials
• ^It is a general term for the variety of things
that result from the presence and flow of
electric charge.^
^Electricity involves
charges trying to find a
balance, just like
everything else in the
world.^
^Lightning^
^A thunderstorm starts as heated moist air in
the atmosphere rises, resulting in the
formation of thunderclouds.^
These clouds grow higher and higher as the
warm updraft continues, carrying the
moisture higher in the atmosphere where it
condenses to form ice crystals.
Since lightning heats the surrounding air
to temperatures hotter than the surface
of the Sun,
there is an EXPLODING sound,
which we call THUNDER.
^Tesla Coil^
• Named after its
inventor, Nikola Tesla
• ^Used to see and study
electricity^
• Can be seen today in
video games and
movies, where the coils
appear as weapons
typically firing bolts of
electricity at enemies^
^Jacob’s Ladder^
• a.k.a high voltage
traveling arc
• ^a device for
producing a
continuous train of
large sparks which
rise upwards^
Learning Outcomes
• Distinguish between static and current electricity,
and identify example evidence of each
• Define electrical discharge providing an example
• Identify electrical conductors and insulators
• Assess the potential danger of electrical devices,
by referring to the voltage and current rating
(amperage) of the device; and distinguish
between safe and unsafe activities
Topic 1
Electrical energy can be transferred and
stored.
*Static Electricity*
• ^A stationary (still; motionless) electric
charge^
• ^a.k.a electrostatics^
• ^an electrical charge caused by an
imbalance of electrons on the surface of a
material^
Examples:
• Hair raising because of a balloon
• Lightning
• Sparks from clothes after they’ve been in
the dryer
This is an example of static
electricity gone bad.
• caused by a refueling fire ignited by static
electricity
^Static is just an
electrical charge that
can be transferred from
place to place.^
^Recall^
• ^An atom is made up of tiny, particles^
• ^Protons: positive charges^
• ^Electrons: negative charges^
^Static Electricity happens when
the charges on the particles cause
either an attractive or repulsive
force between them.^
^If two neutral charges are put together,
there is no movement (attraction or
repulsion).^
*The Laws of Electrical
Charges*
1. ^Like charges repel (keep away from)
one another.^
2. ^Opposite charges attract (pull towards)
one another.^
Remember lightning?
*Charge separation*
^A charged object will also attract to a
neutral or uncharged object.^
^This is also known as Charged
Polarization^
^How does this happen?^
^This happens by causing a concentration
of like charges in specific areas of a
neutral object.^
Ex: A negatively charged ball brought
close to your neutral finger , causes
electrons to repel and protons to come
forward.
*Electrical Discharge*
• ^The sudden transfer of electrical charge
from one object to another, indicated by a
spark.^
^Van de Graaff Generators^
• ^An electrostatic machine which uses a moving
belt to accumulate very high voltages on a
hollow metal globe.^
• 1929, Physicist Robert J. Van de Graaff
• Applications for this high voltage generator
include driving X-ray tubes, food sterilization
and processing, and for nuclear physics
experiments
^ Schematic view^
http://www.youtube.co
m/watch?v=Z77IzaXGcg
Testing your understanding
• You rub your feet across a floor and
electrons transfer from you to the floor.
Are you now negatively or positively
charged?
• A neutral object contains no charge.
Is this statement true or false?
You bring a negatively charged rod close to
some tiny pieces of plastic. Some of the
pieces jump up to the rod, but as soon as
they make contact, they immediately fly
away from the rod.
Explain what happened.
Unit D
Topic 2
^Electric Eel^
• Species of fish (not an eel; knifefish)
• capable of generating powerful electric
shocks, which it uses for both hunting and
self-defense
• has three pairs of organs that produce
electricity
*Electrical Current*
• ^the steady flow (movement) of charged
particles^
• Used to operate electrical devices
^Unlike the charges in static electricity,
which charge and discharge.^
Works under two
conditions:
1. ^Has to have an energy source^
2. ^There must be a *circuit*
(complete path that charged particles need
to flow through)^
The SI (International System) Unit
of electric currents is the *ampere (A)*.
 ^rate at which an electric current flows^
 ^amount of charge per second^
 Specifically, 1 Coulomb of charge per second.
 An ampere can also be called an “amp”.
^Named after André-Marie Ampère, one
of the main discoverers of electromagnetism.^
Current in amps of
Common Electrical
Devices
60-W light bulb = 15 A
Microwave Oven = 5 – 8 A
Electric Kettle = 13 A
Television = 4 – 5 A
TV Antenna Booster = < 1 A
Ceiling Fan = 4 A
A continuous flow of
electrical charge is
easily produced.
It is the transfer of the
charge that is the tricky
part.
*Conductors*
• ^A material that electric charge can move
through easily^
^Conduction of electricity
through wires allows for the
transfer of electrical charge
from place to place.^
Think about an electric
power grid
• Electricity is usually transmitted over long
distance through overhead power transmission
lines.
• Underground power transmission is used only
in densely populated areas (such as large
cities) because of the high cost of installation
and maintenance and because the power
losses increase dramatically compared with
overhead transmission unless superconductors
and cryogenic technology are used.
^Circuits
• ^Since they are complete paths that
charged particles need to flow through,
Circuits control the flow of electricity.^
^Usually they flow along solid metal wires,
but can flow through gases or other
fluids.^
^A circuit may include:
• ^A conductor^
• ^An energy source^
• *Load*
^device in a circuit that converts
electrical energy to another form of
energy^
*Electrical Energy*
• ^Energy of charged particles
• ^It is transferred when electrons travel
from place to place
*Voltage*
• ^A measure of how much electrical energy a
charged particle carries.^
• ^Measured in volts (V)^
Named after Alessandro Giuseppe Antonio
Anastasio Volta; an italian physicist known
especially for the development of the
electric battery in 1800
You will make a battery
in high school…
• ^Volta demonstrated that when metals and
chemicals come into contact with each other
they produced an electrical current.^
• In his research, Volta placed together several
pairs of alternating copper (or silver) and zinc
discs separated by cloth or cardboard and
soaked the cloth or cardboard in brine (salt
water) to increase conductivity, and an
electrical current was produced.
*Potential Difference*
• ^Another name for Voltage^
• ^It is the change in the potential energy of
electric charge compared to its potential
energy at a reference point^
^Energy delivered = Voltage x total charge ^
of electrons
*Voltmeter*
• ^Instrument for
measuring potential
difference in volts^
• If there is more than one
red terminal (positive),
start measuring using the
highest one and work
your way down.
• 1 millivolt = 1/1000 of a volt
1 mV = 0.001 V
Recall Conversion Chart:
km hm dam m dm cm mm
kV hV daV
V dV cV mV
• How does current electricity differ from
static electricity?
• Suppose I have a voltmeter reading 15
mV, convert that to volts.
• You require a high-current battery to start
a large tractor. While shopping for this
battery, should you be more concerned
with the battery’s rating of volts or amps?