Download File - In Class, with Miss. Coates

What is Electricity?
• Electricity is generated from the motion
of tiny charged atomic particles called
electrons and protons!
• Protons = +
• Electrons = electron
neutron
proton
• Electric Charge and Electrical
Forces:
• Electrons have a negative electrical charge.
• Protons have a positive electrical charge.
• These charges interact to create an electrical force.
– Like charges produce repulsive forces – so they
repel each other (e.g. electron and electron or
proton and proton repel each other).
– Unlike charges produce attractive forces – so they
attract each other (e.g. electron and proton attract
each other).
• (A) A neutral atom
has no net charge
because the numbers
of electrons and
protons are
balanced.
• (B) Removing an
electron produces a
net positive charge;
the charged atom is
called a positive ion
(cation).
•
(C) The addition of
an electron produces
a net negative
charge and a
negative ion
(anion).
Electrostatic Charge
• The charge on an ion is called an electrostatic
charge.
• An object becomes electrostatically charged by:
– Friction: Rubbing one object on another object
causes electrons to transfer from one object to the other,
– Conduction: a charged object contacts another object
which results in the transfer of electrons,
– Induction: a charged object comes close to another
object which causes the electrons to be rearranged in the
second object.
Name the form of electrostatic Charging!
• Arbitrary numbers of
protons (+) and
electrons (-) on a
comb and in hair
(A) before and
(B) after combing.
• Combing transfers
electrons from the
hair to the comb by
friction, resulting in
a negative charge
on the comb and a
positive charge on
the hair.
Name the form of electrostatic Charging!
• The comb has become
charged by friction,
acquiring an excess of
electrons. The paper (A)
normally has a random
distribution of (+) and (-)
charges.
• (B) When the charged
comb is held close to the
paper, there is a
reorientation of charges
because of the repulsion of
the charges. This leaves a
net positive charge on the
side close to the comb, and
since unlike charges
attract, the paper is
attracted to the comb.
What is static electricity?
• When two objects rub against each other electrons
transfer and build up on an object causing it to have
a different charge from its surroundings.
• Like the shoes rubbing against the carpet. Electrons
are transferred from the carpet to the shoes.
What causes you to be shocked when you
rub your feet across carpet?
An electrical discharge is the passing of an
electric current through the air from a
negatively charged object to a positively
charge object. This is what causes
lightning!
Electrical Conductors and Insulators:
• Electrical conductors are materials that can
move electrons easily.
– Good conductors include metals. Copper is the best
electrical conductor.
• Electrical nonconductors (insulators) are
materials that do not move electrons easily.
– Examples are wood, rubber etc.
• Semiconductors are materials that
sometimes behave as conductors and
sometimes behave as insulators.
- Examples are silicon, arsenic, germanium.
Current Electricity
An easy way to think of electric current is to picture cars
going through a Turnpike or Parkway Toll.
The cars could represent
electrons or charge, and the
toll booth could represent the
cross sectional area of the
wire at a certain point.
If you counted the number of cars or electrons, that passed through
the toll booth or a certain cross sectional area of the wire, and divided
that number by the time it took for those cars or charges to pass,
you would get the current!
What is the difference between static
electricity and current electricity?
• Static electricity is stationary or collects on the surface of
an object, whereas current electricity is flowing very
rapidly through a conductor.
• The flow of electricity in current electricity has electrical
pressure or voltage. Electric charges flow from an area
of high voltage to an area of low voltage.
Water pressure
and voltage
behave in
similar ways.
There are some similarities between the flow of
water in a pipe and the flow of electric current
through a circuit.
• The pressure of the water flowing through the
pipes on the last slide compare to the voltage
(electric potential) flowing through the wires of
the circuit. The unit used to measure voltage is
volts (V).
• The flow of charges in a circuit is called current.
Current (I) is measured in Amperes (A).
Charge Passing
Through A Given Area
Electric Current = ------------------------------Time
The Ampere
The Ampere is a measure of how
much electrical current is flowing
and is measured in units of amps.
Q
I = ---t
The Ampere
The current varies depending on the force behind
the current and the resistance to flow.
What is electrical resistance?
Resistance (R) is the opposition to the flow of an electric
current, causing the electrical energy to be converted to
thermal energy or light.
The metal which makes up a light
bulb filament or stovetop eye has a
high electrical resistance. This
causes light and heat to be given off.
The unit for measuring resistance is the ohm (Ω).
Resistance and Temperature
Resistance and Thickness
Electric Circuits
– Electric current means a flow of charge in the same way that a
water current flows.
– It is the charge that flows, and the current is defined as
the flow of the charge.
An electrical circuit contains some device that acts as a source of
energy as it gives charges a higher potential against an electrical
field.
The charges do work as they flow through the circuit to a
lower potential.
The charges flow through connecting wires to make a
continuous path.
A switch is a means of interrupting or completing the circuit.
The source of the electrical potential is the voltage source.
A simple electric circuit has a voltage source (such as a
generator or battery) that maintains the electrical
potential, some device (such as a lamp or motor ) where
work is done by the potential, and continuous pathways
for the current to follow.
Voltage Sources - Electricity Relationships
• Generator: creates electrical energy
from mechanical energy
• Batteries (cells): creates electrical
energy from chemical energy
• Motor: conforms electrical energy into
mechanical energy
Battery (cells)
• A battery produces
electricity by
transforming chemical
energy into electrical
energy
Anatomy of a Battery
Carbon Electrode
Zinc Electrode
Sulfuric Acid
What are batteries?
Batteries are composed of a chemical substance which can
generate voltage which can be used in a circuit.
There are two kinds of batteries: dry cell and wet cell batteries.
Below is an example of a dry cell.
The zinc container of the dry
cell contains a moist chemical
paste surrounding a carbon rod
suspended in the middle.
Wet cell batteries are most commonly
associated with automobile batteries.
A wet cell contains two
connected plates made of
different metals or metal
compounds in a conducting
solution. Most car batteries
have a series of six cells, each
containing lead and lead oxide
in a sulfuric acid solution.
What are electric circuits?
Circuits typically contain a voltage source, a wire conductor,
and one or more devices which use the electrical energy.
What is a series circuit?
A series circuit is one which provides a single pathway for the
current to flow. If the circuit breaks, all devices using the circuit
will fail.
What is a parallel circuit?
A parallel circuit has multiple pathways for the current to
flow. If the circuit is broken the current may pass through
other pathways and other devices will continue to work.
What is the difference between an open circuit and
a closed circuit?
A closed circuit is one in which the pathway of the electrical
current is complete and unbroken.
An open circuit is one in which the pathway of the electrical
current is broken. A switch is a device in the circuit in which
the circuit can be closed (turned on) or open (turned off).
Circuit Diagrams
Scientists usually draw electric circuits using symbols;
Circuit Diagrams
Circuit Diagrams
Circuit Diagrams
What is Magnetism
• The magnet is surrounded by an invisible
force field
• All magnets have a North and South POLE
• Opposite poles attracted each other
• All ferrous (containing iron) materials can
be magnetized
• The earth is the biggest magnet around
• Magnetic Fields:
– A magnet that is moved in space near a
second magnet experiences a magnetic
field.
• A magnetic field can be represented by field
lines.
– The strength of the magnetic field is greater
where the lines are closer together and
weaker where they are farther apart.
These lines are a map of the magnetic field around a bar magnet.
The needle of a magnetic compass will follow the lines, with the
north end showing the direction of the field.
• The core is probably
composed of iron and
nickel, which flows as the
Earth rotates, creating
electrical currents that
result in the Earth’s
magnetic field.
• The Earth’s magnetic field
is thought to originate
with moving charges.
The earth's magnetic field.
Note that the magnetic north
pole and the geographic North
Pole are not in the same place.
Note also that the magnetic
north pole acts as if the south
pole of a huge bar magnet were
inside the earth. You know that
it must be a magnetic south
pole since the north end of a
magnetic compass is attracted
to it and opposite poles attract.
What are magnetic domains?
Magnetic substances like iron, cobalt, and nickel are
composed of small areas where the groups of atoms are
aligned like the poles of a magnet. These regions are
called domains. All of the domains of a magnetic
substance tend to align themselves in the same direction
when placed in a magnetic field. These domains are
typically composed of billions of atoms.
• Force Fields:
– The condition of space around an object is
changed by the presence of an electrical
charge.
– The electrical charge produces a force
field, that is called an electrical field since it
is produced by electrical charge.
Hans Christen Oersted
Flux Lines
Electricity and Magnetism
• a wire carrying an electric current always
has a magnetic field around it
– the magnetic field in a straight wire is not
very strong
– if the wire is wound into a coil, the magnetic
field becomes much stronger as the individual
magnetic fields overlap
• the greater the number of coils, the stronger the
magnetic field
Oersted’s Experiment
All magnetic fields originate from moving electric
charges. A magnetic field appears only when relative
motion is present between an electric charge and an
observer. Electric and magnetic fields are different
aspects of a single electromagnetic field.
When a current is run
through a cylindrical coil of
wire, a solenoid, it
produces a magnetic field
like the magnetic field of a
bar magnet. The solenoid
is known as
electromagnet.
Michael Faraday
Electromagnets
• electromagnet – temporary magnet made by
wrapping a current-carrying wire around an iron core
– the center of an electromagnet is called the core
• it is often made of iron
• as long as current is flowing, an electromagnet has a
magnetic field
• when current is turned off, there is no longer a
magnetic field
Joseph Henry’s Bigger and “Badder”
Electromagnet
Strength of Electromagnets
• there are two ways to make an electromagnet stronger
– increasing the number of coils
– increasing the amount of current
• changing the direction of an electric current causes the
poles of an electromagnet to reverse
– this feature is important in the production of electric
motors
An electromagnet consists of an iron core placed
inside a wire coil. The magnetic field strength of a
wire coil carrying an electric current increases in
direct proportion to the number of turns of the coil.
Electromagnets in Your World!
• electromagnets have many important uses
– ex. radios, telephones, computers, electric motors
• electromagnets are useful because they can be turned
on and off
• An electromagnet can be used to
move large quantities of metal. When
the current is on the magnet will pick up
the metal. When you want to drop it you
turn off the power and the electromagnet
is disabled and the metal drops.
In September of 1831, Michael Faraday
made the discovery of Electromagnetic Induction.
Faraday attached two wires to a disc and
rotated the disc between the opposing
poles of a horseshoe magnet creating
an electric current.
If you place a magnet and a conductor (copper wire), in a room together
there will be no electric current generated.
This is because motion, from our equation for electricity, is missing!
An electric current is not generated unless the magnetic field is moving
relative to the copper wire, or the copper wire is moving relative to the
magnetic field.
Magnetic Force on a Current
A magnetic field exerts a
sideways push on an
electric current with the
maximum push occurring
when the current is
perpendicular to the
magnetic field. Currents
exert magnetic forces on
each other. The forces are
attractive when parallel
currents are in the same
direction and are repulsive
when the parallel currents
are in opposite directions.
Electric Motors
An electric motor uses
the sideways push of a
magnetic field to turn a
current-carrying wire
loop. Electric motors
use a commutator to
change the direction of
the current in the loop.
Alternating current
electric motors do not
use commutators.
So simple electric generators found in power plants contain, magnets and copper
wire that when put into motion relative to one another create the electric current
that is sent out to homes.
The major problem in
electricity generation is
where does the motion
come from that keeps the
copper wire and magnets
moving relative to one
another.
In this case, wind power applies a force to the blades that turns them. The spinning
blades, spin an armature that turns the copper wire relative to the magnetic field. As
long as the blades spin, electricity will be generated!
Types of Sources used to make Electricity
•
•
•
•
•
•
Thermal
Geothermal
Nuclear
Hydroelectric
Solar
Wind
Pictures of each Source
-Solar Power – uses the sun energy to either boil water or directly
converts solar energy to electrical energy
-Ocean Thermal Energy Conversion – uses temperature differences
between different depths of ocean water to drive a heat engine. Working
fluid is ammonia which is gas at room temperature.
-Biomass Energy: Municipal Solid Waste – burning wastes to drive heat
engines
-Geothermal Energy – based on naturally occurring heat in the Earth in
the Earth due to radioactive decay
-Tidal Energy – uses the gravitational pull of the moon on our oceans to
drive turbines
Proportion of World’s energy
consumption - 1997
Proportion of the world’s
Electricity generation - 1997
Saskatchewan’s
Electricity
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How do we get Electricity?
• Energy from one of the sources is converted by
machines at the power plant to Electricity and then put
onto the Electric Power Grid
• Electric Power Grid
– Power Plants
– Transmission Lines
– Substations
– Power Lines
– Transformers
– Electrical Wiring and Circuit Box
Pictures of each piece of the Power Grid!
Electrical Energy
Electricity by definition is electric current that is used as a power source!
This electric current is generated in a power plant, and then sent out
over a power grid to your homes, and ultimately to your power outlets.
What happens at Home?
At home, electric current
that was generated by
generators in the power
plant is used to power
electric appliances.
The electric current,
running through the
copper wire causes
the armature to spin
which is how most
motors generate
motion.
This meter measures the amount of electric work done
in the circuits, usually over a time period of a month. The
work is measured in kWhr.
Electric Power
The power of an electric current is the rate at which
it does work and is equal to the product of the
current and the voltage of a circuit:
The unit of electric power is the watt.The
commercial unit of electric energy is the
kilowatthour (kWh).
Electric Power
Typical Power Ratings
Appliance
Stove
Clothes Dryer
Heater
Dishwasher
Photocopier
Iron
Vacuum Cleaner
Coffee Maker
Refrigerator
Portable Sander
Fan
Personal Computer
TV Receiver
Fax Transmitter/Receiver
Charger for Electric Toothbrush
Power (W)
12,000
5,000
2,000
1,600
1,400
1,000
750
700
400
200
150
150
120
65
1
How is household wiring arranged?
Most household wiring is logically designed with a combination
of parallel circuits. Electrical energy enters the home usually at
a breaker box or fuse box and distributes the electricity
through multiple circuits. A breaker box or fuse box is a
safety feature which will open
How is Electrical Power calculated?
Electrical Power is the product of the current (I) and the
voltage (v)
The unit for electrical power is the same as that for
mechanical power– the watt (W)
Example Problem: How much power is used in a circuit
which is 110 volts and has a current of 1.36 amps?
P=IV
Power = (1.36 amps) (110 V) = 150 W
Electric current generation - whether from fossil fuels, nuclear,
renewable fuels, or other sources is usually
based on the:
Careers in the Field of Electricity
http://learn.org/articles/What_are_Some_Common_Careers_in_the
_Electricity_Industry.html
Videos/Animations
• http://ippex.pppl.gov/interactive
/electricity/static.html
• http://videos.howstuffworks.co
m/hsw/19720-electricity-andmagnetism-creating-electricityvideo.htm