Magnets
What is a magnet? A magnet is a body which attracts iron, combinations of metals
(known as alloys) or other materials which are composed of iron or iron-like substances.
"Attract" means an object composed of iron will attach or affix itself to the magnet.
Additionally, the magnet can "magnetize" other objects which in turn act like magnets.
Other iron objects will be attracted to the magnetized object.
The two ends of the magnet are different and are referred to as the north and south
pole (or north-seeking pole and south-seeking pole). Like poles repel. The south poles of two
magnets will not attract one another. Neither will the north poles of two magnets. The north
pole of one magnet and the south pole of another magnet will attract one another.
Like Poles Repel –
Unlike Poles Attract
http://www.swe.org/iac/lp/magnets_03.html
Bar Magnet
MAGNETS AND ELECTRICITY
In most objects, all of the forces are in balance. Half of
the electrons are spinning in one direction; half are
spinning in the other. These spinning electrons are
scattered evenly throughout the object.
Magnets are different. In magnets, most of the electrons
at one end are spinning in one direction. Most of the
electrons at the other end are spinning in the opposite
direction.
This creates an imbalance in the forces between the ends
of a magnet. This creates a magnetic field around a
magnet. A magnet is labeled with North (N) and South (S)
poles. The magnetic force in a magnet flows from the
North pole to the South pole.
Have you ever held two magnets close to each other? They
don’t act like most objects. If you try to push the South poles
together, they repel each other. Two North poles also repel
each other.
Turn one magnet around and the North (N) and the South (S)
poles are attracted to each other. The magnets come together
with a strong force. Just like protons and electrons, opposites
attract.
These special properties of magnets can be used to make electricity. Moving magnetic fields can pull and
push electrons. Some metals, like copper have electrons that are loosely held. They can be pushed from
their shells by moving magnets. Magnets and wire are used together in electric generators.
http://www.eia.doe.gov/kids/energyfacts/sources/electricity.html
Magnets
A magnet has two poles, called North and South.
A magnetic field is a region around the magnet
where magnet materials experience a force.
There are only three magnetic elements, iron, nickel and cobalt.
In practice you will only use iron,
or steel which is an alloy of iron
The shape of the magnetic field around the magnet is shown by lines.
Arrows on the lines point away from North and towards South
to show the direction of the magnetic field.
Notice that the lines of magnetic force do not cross each other.
The closer together the lines are, the stronger the field is.
You need to know the shape of the magnetic field for a bar magnet,
poles which attract and poles which repel.
The magnetic field can be seen by placing the magnet
under a piece of paper with small iron filings on top.
The filings line up in the shape of the field, as shown above.
The direction of the arrows can be seen by placing a compass in the field.
The compass points in the direction of the arrows,
away from North and towards South.
Note - this means that when a compass points to the Earth's North Pole,
there must be a magnetic South Pole up there
(bet that confuses the penguins!). http://www.gcsescience.com/pme1.htm
The Loop
Closed Vs. Open Circuit
Loads
BATTERIES PRODUCE ELECTRICITY
A battery produces electricity using two different metals in
a chemical solution. A chemical reaction between the metals and
the chemicals frees more electrons in one metal than in the other.
One end of the battery is attached to one of the metals; the other
end is attached to the other metal. The end that frees more
electrons develops a positive charge and the other end develops a
negative charge. If a wire is attached from one end of the battery
to the other, electrons flow through the wire to balance the
electrical charge. A load is a device that does work or performs a job. If a load––such as a light
bulb––is placed along the wire, the electricity can do work as it flows through the wire. In the
picture above, electrons flow from the negative end of the battery through the wire to the
light bulb. The electricity flows through the wire in the light bulb and back to the battery.
http://www.eia.doe.gov/kids/energyfacts/sources/electricity.html
ELECTRICITY TRAVELS IN CIRCUITS
Electricity travels in closed loops, or circuits (from the word circle). It must have a complete
path before the electrons can move. If a circuit is open, the electrons cannot flow. When we flip
on a light switch, we close a circuit. The electricity flows from the electric wire through the
light and back into the wire. When we flip the switch off, we open the circuit. No electricity
flows to the light. When we turn a light switch on, electricity flows through a tiny wire in the
bulb. The wire gets very hot. It makes the gas in the bulb glow. When the bulb burns out, the
tiny wire has broken. The path through the
bulb is gone. When we turn on the TV,
electricity flows through wires inside the
set, producing pictures and sound.
Sometimes electricity runs motors—in
washers or mixers. Electricity does a lot of
work for us. We use it many times each
day.
http://www.eia.doe.gov/kids/energyfacts/sources/electricity.html
Electromagnet
Electromagnets are usually in the form of iron core solenoids. The
ferromagnetic property of the iron core causes the internal magnetic
domains of the iron to line up with the smaller driving magnetic field
produced by the current in the solenoid. The effect is the
multiplication of the magnetic field by factors of tens to even
thousands. The solenoid field relationship is
and k is the relative permeability of the iron, shows the magnifying
effect of the iron core.
http://media.fwbell.com/mag.html
How do I make an electromagnet?
It is fairly easy to build an electromagnet. All you need to do is wrap some insulated copper wire around
an iron core. If you attach a battery to the wire, an electric current will begin to flow and the iron core
will become magnetized. When the battery is disconnected, the iron core will lose its magnetism. Follow
these steps if you would like to build the electromagnet described in our Magnets and Electromagnets
experiment:
Step 1 - Gather the Materials
To build the electromagnet described in our Magnets and Electromagnets experiment, you will need:
One iron nail fifteen centimeters (6 in) long
Three meters (10 ft) of 22 gauge insulated, stranded copper wire
One or more D-cell batteries
A pair of wire strippers
Step 2 - Remove some Insulation
Some of the copper wire needs to be exposed so that the battery can make a good electrical connection.
Use a pair of wire strippers to remove a few centimeters of insulation from each end of the wire.
Step 3 - Wrap the Wire
Around the Nail
Neatly wrap the wire
around the nail. The more
wire you wrap around the nail, the stronger your electromagnet will be. Make certain that you leave
enough of the wire unwound so that you can attach the battery.
When you wrap the wire around the nail, make certain that you wrap the wire all in one direction. You
need to do this because the direction of a magnet field depends on the direction of the electric current
creating it. The movement of electric charges creates a magnetic field. If you could see the magnetic
field around a wire that has electricity flowing through it, it would look like a series of circles around
the wire. If an electric current is flowing directly towards you, the magnetic field created by it circles
around the wire in a counter-clockwise direction. If the direction of the electric current is reversed,
the magnetic field reverses also and circles the wire in a clockwise direction. If you wrap some of the
wire around the nail in one direction and some of the wire in the other direction, the magnetic fields
from the different
sections fight each
other and cancel out,
reducing the strength
of your magnet.
Step 4 - Connect the
Battery
Attach one end of the
wire to the positive
terminal of the battery and the other end of the wire to the negative terminal of the battery. If all has
gone well, your electromagnet is now working!
Don't worry about which end of the wire you attach to the positive terminal of the battery and which
one you attach to the negative terminal. Your magnet will work just as well either way. What will change
is your magnet's polarity. One end of your magnet will be its north pole and the other end will be its
south pole. Reversing the way the battery is connected will reverse the poles of your electromagnet.
Hints to Make Your Electromagnet Stronger
The more turns of wire your magnet has, the better. Keep in mind that the further the wire is from the
core, the less effective it will be.
The more current that passes through the wire, the better. Caution! Too much current can be
dangerous! As electricity passes through a wire, some energy is lost as heat. The more current that
flows through a wire, the more heat is generated. If you double the current passing through a wire, the
heat generated will increase 4 times! If you triple the current passing through a wire, the heat
generated will increase 9 times! Things can quickly become too hot to handle.
Try experimenting with different cores. A thicker core might make a more powerful magnet. Just make
certain that the material you choose can be magnetized. You can test your core with a permanent
magnet. If a permanent magnet is not attracted to your core, it will not make a good electromagnet. An
aluminum bar, for example, is not a good choice for your magnet's core.
Gravity
Gravity is a force that for us is always directed
downwards. But to say that gravity acts downwards is
not correct. Gravity acts down, no matter where you
stand on the Earth. It is better to say that on Earth
gravity pulls objects towards the centre of the Earth.
So no matter where you are on Earth all objects fall to
the ground
See the diagram:
What is gravity?
Gravity is a force that attracts objects
together. On earth this force attracts
everything to Earth.
The strength of gravity.
The Earth is a very large object and it is also very heavy. This means that it
has got a strong gravitational field.
The moon is smaller than the Earth and is not as heavy.
Would you expect its gravity to be stronger or weaker than the Earth's
gravity?
Famous People & Electricity!
Benjamin Franklin
Ben Franklin harnessed electricity by
flying a kit with an iron key attached to
the string. Franklin was a curious man,
and he experimented during
thunderstorms until he invented the
lightning rod. He also invented bifocal
glasses, and the Franklin stove.
Benjamin Franklin signed the Declaration
of Independence, and several other important documents.
Franklin was certainly a well-rounded man!
Michael Faraday
The Quarterly Journal of Science and the Arts (1818)
The son of an impoverished blacksmith, Faraday was apprenticed as a
bookbinder. He read every book he bound. After securing menial work at the
Royal Institution, Faraday went on to discover electromagnetic induction, the
battery and the dynamo. He did pioneering work in electrochemistry, isolated
benzene and produced aluminum by electrolysis. He built the first electric
motor, and later the first generator and transformer.
Thomas Edison
The inventor Thomas Alva Edison (in the USA)
experimented with thousands of different
filaments to find just the right materials to glow
well and be long-lasting. In 1879, Edison
discovered that a carbon filament in an oxygen-
free bulb glowed but did not burn up for 40 hours.
Edison eventually produced a bulb that could glow
for over 1500 hours.
STATIC ELECTRICITY
Electricity has been moving in
the world forever. Lightning is a
form of electricity. It is
electrons moving from one cloud
to another or jumping from a
cloud to the ground. Have you ever felt a shock when
you touched an object after walking across a
carpet? A stream of electrons jumped to you from
that object. This is called static electricity.
Have you ever made your hair stand straight up by rubbing a
balloon on it? If so, you rubbed some electrons off the balloon. The
electrons moved into your hair from the balloon. They tried to get
far away from each other by moving to
the ends of your hair.
They pushed against each other and
made your hair move—they repelled
each other. Just as opposite charges
attract each other, like charges repel
each other.
Static Electricity Experiment
Image right: Static electricity from a balloon really makes an empty soda can
move! Credit: NASA
You will need:
balloons
empty soda can
string (if you like)
Here's what you do:
1. Blow up the balloon.
2. Rub the balloon on your head. This makes an electrical charge.
3. Lay the soda can on a smooth floor.
4. Bring the balloon close to the can.
5. Look at what happens.
6. Have a race with a friend with two cans and two balloons. See who can move the can across the
room first, without touching it.
7. Try rubbing the balloon on your hair and then sticking it to a wall.
8. Tie string to the ends of two balloons that you have blown up.
9. Rub the two balloons together.
10. Hold them by the strings right next to each other.
11. Watch what happens.
Image above: Static
electricity makes your
hair stand up Credit:
NASA
Lightning - The Great Mystery
In an electrical storm, the storm clouds are charged like giant capacitors in the sky. The upper
portion of the cloud is positive and the lower portion is
negative. How the cloud acquires this charge is still not
agreed upon within the scientific community, but the
following description provides one plausible explanation.
In the process of the water cycle, moisture can
accumulate in the atmosphere. This accumulation is
what we see as a cloud. Interestingly, clouds can contain
millions upon millions of water droplets and ice
suspended in the air. As the process of evaporation and
condensation continues, these droplets encounter many collisions with other moisture that is in
the process of condensing as it rises. Also, the rising moisture may collide with ice or sleet that
is in the process of falling to the earth or located in the Capacitors
lower portion of the cloud. The importance of these A capacitor is an electrical device that
collisions is that electrons are knocked off of the rising consists of two conductive surfaces
separated by an insulating (dielectric)
moisture, thus creating a charge separation.
media. When a voltage is applied to the
surfaces, energy is stored in the
The newly knocked-off electrons gather at the lower
resulting electric field created by the
portion of the cloud, giving it a negative charge. The charge separation of the surfaces.
rising moisture that has just lost an electron carries a
positive charge to the top of the cloud. Beyond the You can create a simple capacitor by
collisions, freezing plays an important role. As the rising separating two sheets of aluminum foil
with a sheet of plastic wrap. The
moisture encounters colder temperatures in the upper
quality of the capacitor is controlled
cloud regions and begins to freeze, the frozen portion by the size of the two pieces of foil,
becomes negatively charged and the unfrozen droplets the insulating quality of the plastic and
become positively charged. At this point, rising air the thickness of the plastic -- the
currents have the ability to remove the positively closer the two pieces of foil, the
charged droplets from the ice and carry them to the top better the capacitor. A good, large
capacitor can easily store enough
of the cloud. The remaining frozen portion would likely
electricity to melt a screwdriver!
fall to the lower portion of the cloud or continue on to
the ground. Combining the collisions with the freezing, we A cloud acts like a huge capacitor. The
can begin to understand how a cloud may acquire the top and bottom of the cloud are like
extreme charge separation that is required for a the two pieces of foil. Huge amounts of
electricity can be stored inside this
lightning stroke.
cloud capacitor.
Series & Parallel Circuits
There are 2 ways to connect multiple devices to a power source (e.g. speakers to an amplifier), series and
parallel. Well... OK, there's also series/parallel. But we'll cover that on a later section.
Speakers in series
In a series circuit (like the two above), the current must flow through one device to get to the next device. This
means that the rate of current flow through all devices is the same. The voltage across each device depends on its
impedance/resistance of each device and the current flowing through the circuit. When adding more components
in a series circuit, the current flow decreases, if the applied voltage remains
constant.
Example of Series Circuits : Christmas lights (when one goes out they all
go out)
Speakers in parallel
In a parallel circuit (like the two examples above), each device is directly connected to the power source. This
means that each device receives the same voltage. The amount of current flowing through each device is
dependent on the impedance/resistance of that particular device. If devices are
added to the power source in a parallel configuration, the current demand/flow from
the power source increases.
Examples of Parallel Circuits: Computer (the electricity flows to each item in the computer to make it
work)
http://www.bcae1.com/srsparll.htm