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Electricity and Magnetism
It’s An Electric World
There are many natural and manufactured objects that use
electricity.
Natural occurring electricity would be electricity such as
lightning, electric eels, electric rays, electric catfish, static
electricity, brain and nerve impulses. This electricity happens
by itself in nature.
The electricity used by humans which is manufactured
would include electricity such as toasters, light bulbs, fans,
cars, electric construction tools, clocks, school buzzers,
and electromagnets for moving scrap metal. This is most
commonly known as current electricity.
Natural Electricity
Static electricity is created whenever a
material with loosely bonded electrons (hair, fur, nylon, silk)
rubs against a non-conducting material that strongly attracts
electrons (plastic, rubber) in a relatively dry environment.
Moisture in the air (humidity) discharges static electricity
as it is created.
Lightning is caused by electrical discharge released from a
thundercloud that has become electrically imbalanced. As
thunderclouds churn, positive charges (protons) accumulate
near the top of the cloud while negative charges (electrons)
concentrate near the bottom. The separation of charges makes
the cloud electrically imbalanced within itself, as well as in
relation to the other clouds around it, or the ground. Lightning
results when the electrical imbalance equalizes itself (negative
charges jump to adjacent positively charged objects). The flash
we see is caused by molecules of air that are heated by friction
to the point of glowing. Heated air along the path of lightning
expands and contracts quickly, creating sound waves (thunder).
Plants use an electrical force (about 0.1 V) to obtain
nutrients from the soil and draw them up into their root cells.
Some plants use electricity to respond to touch (mimosa plant
leaves close up when touched). The coiling of tendrils of
climbing plants is also thought to be an electrical response.
Electric eels and other electric fish have organs along the
sides of their bodies that build up a charge that can be used for
sensing their environment, protecting themselves against
predators, and obtaining food. Electric eels can produce a
charge up to 600 volts, which is enough to light up ten, 40 watt
light bulbs. This voltage is strong enough to stun organisms as
large as a horse or a human, causing them to stop breathing and
therefore drown. Sharks and rays communicate using electric
signals, which other fish can pick up in the water.
The human body runs on electricity that is generated when
different electrically charged particles move between cells and
surrounding fluids in the body. Everything you do depends on
tiny electrical impulses of about 0.1 V traveling through your
body. Your brain operates on approximately 10 watts of
electricity, the same amount required to light up a string of
outdoor Christmas lights. Injuries heal faster because an
electrical current begins to flow from a cut or wound which
trigger cell division and makes nerves in the injured area grow
faster. Your brain, nervous system, and muscles work because
of electricity. Your nerves act like a telephone line transmitting
tiny electrical impulses to and from your brain, however, the
amount of electricity used to send these messages is not
enough to light a tiny LED (light-emitting diode that generally
uses less than 2V).
Current Electricity
A larger electrical current, such as the 120 V household
current, will override your body's low voltage causing a
disruption of message transmission. Thus a shock from an
electrical appliance may cause the muscles and brain to stop
functioning and cause death.
Please remember not to attempt any investigation, at home
or at school, using the electrical current provided by the wall
outlets (plug ins) or any electrical devices that use the
household power supply.
There are dangers associated with current electricity and
care should be taken to avoid short circuits. Short circuits may
cause wires to heat up and can start fires.
Safety Rules
Electrons are always looking for the shortest, easiest
pathway to the ground. Electricity will leave the wires or
electrical device if it can find an easier path to follow. Our
bodies are 70% water ( a good conductor of electricity) and so
humans can become the shortest pathway to the ground if we
come in contact with an electrical current and the ground ( or
something touching the ground such as a tree or ladder) at the
same time.
Hot Stuff
The electricity produced by a D-cell battery is totally safe
and is not strong enough to harm anyone. You will feel heat
generated when two terminals of the battery are connected.
Without a load, (such as a light bulb), to provide resistance,
electrons flow and create friction with the material in the wire,
and so cause the wire to heat up. If you keep the wire connected
to the battery without a load, you will drain the battery of its
energy.
In A Flash-Burning Steel Wool
The electricity flowing through the battery and steel wool
had no resistance (load) to pass through. The friction of the
moving electrons was sufficient to heat up the steel wool and
cause it to burn.
Lights On!
Will It Light?
A bulb will light whenever the electric current produced by
the battery can flow from the battery through the bulb and back
to the battery. The flow of the electrons is from the negative (-)
terminal to the circuit and back to the positive (+)
Bulbs
Electrons flow in through the metal at the side-bottom of
the bulb. Then the electrons flow up the wires in the support
towers and through the filament (thin, curly wire), which glows.
Electric energy is changed into light energy. Electricity flows
out through the metal bump at the very bottom of the bulb. The
air inside the glass bulb has been taken out at the factory and
replaced with a gas (argon). This prevents the filament from
burning out too quickly.
The electric current can enter the bulb through either of the
lead contacts. Electricity is conducted across the threaded
base, to the lead contact, up the support, across the filament,
down the other support, and out through the other lead contact
back into the circuit. The direction of electrons’ flow can be
opposite to the above, depending on which way the bulb is
connected to the battery. The insulating ceramic disc separates
the threaded base and lead contact on the bottom of the base
preventing a short circuit.
More Wires
There is a method of shorthand that is used for electrical
drawings. This method is useful in that it minimizes the time
required to draw, and it is universal because it is understood by
everyone who knows the symbols.
Light Sockets and Battery Holders
There are many ways to open and close circuits. Electrons
prefer to travel through “the path of least resistance” rather than
travel through the bulb. Please take care not to touch the wires
together as a short circuit will be created and the bulb will go
out.
Open and Closed Circuits
When we hear the word circuit, it brings to mind certain
other words, such as “circle”, cycle, etc. It means that
something is in an unbroken line. An open circuit is one which
does NOT allow a complete path for the electricity to flow
through. A closed circuit is one that does allow a complete path
and causes the bulb to light.
If the wires in your home were to touch each other, then
the current traveling through the wires is able to produce
enough heat to produce a fire. This is why it is very important
not to use an appliance with a torn or frayed cord.
Bare copper wire (that is, not coated with a plastic or
rubber coating) might have a clear insulation sprayed onto it,
and as a result will not conduct electricity. If you want to
conduct electricity then you may want to sand the edges of the
wire to remove the coating.
Short Circuits
Always be very careful when working with wires and
batteries. The bare ends of the wires can become extremely hot
if they touch.
Shorted circuits will quickly drain a battery. There is heat
generated in a short circuit, by the friction between electrons in
the wire. A short circuit is when there is a "short cut" for
electrons to avoid passing through the load (e.g. light bulb) After
all experiments dealing with electricity, please disconnect wires
from dry cells.
Usually electricity will follow the easiest, shortest path
back to its source. This is known as the "path of least
resistance." If electricity is allowed to flow for more than a few
minutes, the wires will begin to heat up. The "easier" path
created (no load) allows too much current to flow, heating up the
wires. You can apply this concept to the 120 V current used in
homes and businesses, not to mention the appliance cords
when they are frayed or cracked. THE HEAT GENERATED
COULD CAUSE A FIRE!!!!
Fuses prevent circuits from overheating and causing fires.
A fuse prevents a fire by melting and breaking the circuit before
the wires get too hot.
Making a Switch
A complete circuit is comprised of a power source, a
switch to control the power flow, connectors through which the
current can flow, and a load (e.g. light bulb, motor, heater, etc.)
Two-way switches can turn a light on or off, either upstairs,
or downstairs. This particular circuit requires two double-pole
switches which will look like this:
Add a Battery
When the positive terminal of one battery is connected to
the negative terminal of another battery, this is known as a
series connection. Batteries connected in a series will cause the
bulb to glow brighter and the current must flow through both
batteries to the load and back. Any opening of a connection will
cause the bulb to go out. In the series connection, the bulb will
burn brighter, but will not last as long as in a parallel
connection.
If the positive terminal of a battery is connected to the
positive terminal of another battery, and the negative terminal of
the batteries are also connected to each other, this is a parallel
connection. Batteries connected in parallel will not affect the
brightness of the bulb and when one battery is taken out of its
holder the bulb will continue to glow. In the parallel connection
the bulb should burn for twice as long as a circuit containing
just one battery.
In the old days, Christmas lights were wired in series and if
one light bulb went out, the lights on the entire string would go
out.
Lights are now wired in parallel which means that the current
has more than one path to follow, so it one bulb goes out, the
rest of the string will continue to burn. The same principle holds
for batteries in series and parallel connections. In a series there
is only one path for the current to follow. In parallel, the current
has more than one path to follow.
Illustrations:
Series Wiring:
Parallel Wiring:
A Magnetic Experience
Please be careful not to burn your skin during this activity
because the wire will heat up as electricity flows through it. If no
battery holder is available, then the wire ends should be taped
firmly to the end of the battery rather than holding them in place
with bare fingers.
Usually, an electromagnet is a coil of wire with an iron bar
tucked inside. When an electric current flows through a wire, a
magnetic field is produced around the wire.
A magnetic field is associated with moving electrons so a
flow of electrons, as in a current, will have a magnetic field
associated with it. The greater the flow of electrons, the
stronger the magnetic field that surrounds the wire. Therefore,
adding cells in series, makes the electromagnet stronger.
Increasing the number of coils of wire also concentrates the
magnetic field, as does the iron rod around which the wire is
coiled. Using the other non-magnetic metals or other
substances does not affect the strength of the magnetic field.
Reversing the direction of the coils on the nail cancels out the
magnetic field. Electromagnets are used to pull switches off
and on, particularly when we do not want to get near extremely
powerful currents. Electromagnets turn automatic devices such
as refrigerators, street lights, and electric hot water heaters on
and off at the appropriate times.
Illustration:
The Coil and the Magnet
Galvanometers are used to detect and measure electric
currents. The needle can be placed on a dial that indicates the
strength of the current. Converting magnetism into electricity is
called magnetic induction. Michael Faraday first discovered this
in the early 1800’s. All generators that produce electricity in
vehicles and power plants work on this principle.
A Field to Remember
To check for magnetic fields, iron filings or a compass can
be used. If you are using a compass, place the compass needle
at various spots around the bar magnet, and record the direction
of the compass needle.
The same can be done around a single wire carrying a current or
around an electromagnet. If a single wire is used, it could be
passed through a piece of cardboard before it is connected to
the battery. The compass then can be placed at spots around
the vertical wire and the needle direction is written down.
Magnetic force extends out from a magnetized object to
one carrying a current forming what is called a magnetic field.
This invisible force field can be made visible indirectly by the
use of particles, such as iron filings. The rule is that the greater
the number of magnetic field lines, the greater the strength of
the magnetic field. On a bar magnet, the number of lines is
generally most concentrated at the poles where the strength of
the magnet is greatest. In a coil of wire making up an
electromagnet, the magnetic field lines are most concentrated
through the coil, and pass out at each end.
Illustrations:
Bar Magnet:
Electromagnet
Making an Ammeter
An ammeter is device used to detect and measure the flow
of electricity. There is electricity when there is evidence of
magnetic fields around magnets and around current-carrying
wires, by use of iron filings or by use of one or more
compasses.
All Conductors Don’t Drive Trains
Materials that will complete a circuit are called conductors
and materials that make it difficult for electricity to travel
through are known as insulators.
Certain atoms will hold onto their electrons very tightly
(rubber and plastic). Other atoms allow their electrons to move
freely from one atom to the next (most metals). Materials that
hold their electrons tightly do not permit electricity to flow and
are called insulators. Conductors are just the opposite with
freely moving electrons allowing electricity to flow easily.
Item such as nails, paper clips, scissors, keys, tacks, pins,
dimes, nickels, foil, etc., conduct electricity. Metals are
conductors of electricity.
Materials such as plastic, glass, chalk, wood, styrofoam
(nonmetals) do not conduct electricity. Most non-metals are
non-conductors of electricity.
Some common insulators are: rubber, glass, plastic.
Rubber is used to make gloves for electricians. Plastic coatings
insulate many wires.
Good conductors include: copper, silver, and salt water.
Most wiring is made of copper.
Non-conductors, or insulators, help us to use electricity
safely. Some examples of this are: insulation around a power
cord, insulated handle on an electric teakettle.
You must be very careful when using electricity around a
conductor (e.g. using a radio in the bathroom).
Some materials act as insulators in certain situations, but
can conduct electricity when more batteries are used. For
example, under low voltage circumstances, tungsten will act as
an insulator and will not allow electrons to move through it.
With higher voltage, more energy is available to push the
electrons through the tungsten and it acts as a conductor. All
materials will conduct an electric current to some extent at
certain voltages or temperatures. An example of this is air,
which is normally a good insulator. Air may conduct electric
charges when the voltage is high enough (e.g. lightning). A
vacuum seal is the only perfect insulator.
Insulation in appliances and cords prevents shocks and
short circuits.
Liquid Conductors or Insulators
If you add salt to water, and attach batteries to wires that
are then dipped into the water, you will notice bubbles forming
around the wires. The bubbles indicate, that even if there is not
enough electric current to light a light bulb, there is enough
current to cause a chemical reaction around the electrodes
(wires). The electricity is splitting water molecules into oxygen
and hydrogen.
Using electricity around water, or handling devices with
wet hands, is dangerous. Also, the human body is 70% water
(and salt), so if you touch electricity, it will flow through you.
You could be badly hurt.
Liquids that contain a noticeable acid, base, or salt are
good conductors of electricity. Liquids with only trace amounts
of acids, bases, or salts are poor conductors, but may conduct
electricity if the voltage is high enough.
Resistance Wires
Bare copper wire (not coated with plastic coating) may
have a clear insulation sprayed on it and as a result it will not
conduct electricity. Sanding the ends of the wire with
sandpaper will remove the clear insulation.
Nichrome wire does not conduct electricity like copper
wire. The nichrome is a resistor. A resistor is something that
slows down the flow of electrons and so makes them lose
energy (heat and light).
Some devices in homes that use resistance wire are:
dimmers, switches, toasters, stoves, irons, and bulbs. The
current passes through a great length of resistance wire, and so
causes the electrons to “fade out” ” losing their heat or energy.
Turn It Up!
The nichrome wire does not allow electrons to pass
through it as freely as the copper wire does. The greater the
length of nichrome wire the current is forced to ass through, the
greater the "resistance"; fewer insufficient electrons pass
through to light the bulb.
A Pencil Resistor
Graphite, as used in the centre of a pencil, does not
conduct electricity as well as metal in wire. Electrons will flow
into the graphite, but will have a difficult time moving through it;
thereby losing some of its energy. There is less voltage left to
light the bulb, which makes it glow dim. The longer the graphite
path, the lower the voltage. Eventually, the voltage will be too
low to light the bulb at all. Applications of this concept are
found in volume controls and dimmer switches.
Testing the System
There are many variables that affect the way an electrical
device behaves when connected in a circuit. Some of these are:
a)
the number of batteries
b)
voltage of the batteries
c)
number of bulbs
d)
type of bulb
e)
the material from which wires are made
f)
length of wires
g)
thickness/thinness of wires
Measuring Electricity Usage
Learning how to read a household electrical meter helps
you to understand your electricity bill. The unit of measure used
is the kilowatt-hour (kW).
Different devices have different wattages because the
wattage is related to the job the device does. To produce
enough heat to cook food, a stove must convert a lot of
electrical energy into heat energy (notice that all heating and
cooling devices have a large wattage). Therefore, it requires a
large power supply (it has a high wattage). A clock on the other
hand, only needs enough electrical energy to allow its tiny motor
to move the hands of the clock. A device draws power based on
the amount of energy it needs to work.
An interesting fact: The Grand Coulee Hydroelectric Power
Plant, located on the Columbia River in the United States,
produces 6 million ( 6 000 000) kilowatts of electric power each
second.
Calculation of Electricity Consumed
To calculate the amount of electricity consumed by an
appliance, multiply the amount of electricity it demands by the
length of time it operates.
e.g. If the light bulb in your bedroom demands 100 watts
and it is on for 10 hours, it consumes:
100 watts x 10 hours = 1000 watt-hours of electricity=1 kilowatthour (kWh)
If you were measuring the distance between Edmonton and
Calgary, you would not use millimetres. The larger kilometre
unit is more appropriate. Since the watt is a very small unit of
measure, it is necessary to convert it to the much larger unit of
the kilowatt. A kilowatt is 1000 watts. To convert the wattage of
your devices into kilowatts, you divide the number of watts the
device uses by 1000. That is you move the decimal three spaces
to the left.
The total amount of energy used over a period of time by
all the electrical devices in your home can be measured by using
a household energy meter.
To read a household meter, it is important to understand
how the dials rotate. The pointer on the first dial rotates
clockwise; the second pointer rotates counterclockwise, the
third turns clockwise, and so on. As the right dial turns a full
revolution, it pushes the next dial causing it to turn. The dial on
the right must rotate 10 times before the dial on the left rotates
once. This is true of each dial in the sequence.
To take a meter reading, copy the numbers indicated by the
pointers from right to left because the dial readings change from
right to left. You want to stay head of any number changes. If
the pointer is between two numbers, copy the lower number. If
the number is between 0 and 9, record the 9. Be sure to record
all zeros to hold their place value.
How Efficient Are You?
There is a need to conserve energy to save non-renewable
resources and money, and decrease pollution. It is also very
important to see that you, by yourself, can make a difference
through your own behaviour and through your influence on the
behaviour of others.
Make a list of things you can do to help save energy:
1.
2.
3.
4.
Turn off electrical devices when they are not in use.
Use natural sunlight as a source of energy.
Shop and compare when purchasing electrical
equipment.
Use fluorescent lighting instead of incandescent
lights, as they can save up to 75 % of lighting costs.
It’s Up to You!