Transcript Magnet

Magnetism
Khan video Magnetism
1. What causes a compass to 1.
behave as it does?
• Earth’s gravity
• Earth’s shape
• Earth’s geographic north
pole
• Earth’s magnetic field
Earth’s magnetic
field…causes a
compass to
behave as it does
2. Magnetic poles that are
alike
• attract each other
• repel each other
• do not interact
• have the same shape
2.
Magnetic poles
that are
alike…repel each
other
3. As in the case of unlike
magnetic poles, unlike
electric charges
• attract each other
• repel each other
• exist in pairs
• do not interact
3.
Unlike electric
charges...attract
each other
History of Magnetism
• 2000+ years ago
– Greeks near the city of Magnesia
found strange and rare stones with
the power to attract iron—called
them magnetite (Fe3O4)
– Lodestone- naturally magnetized
piece of magnetite
• 1000 years ago
– Chinese stroked a steel needle with
“lodestone” (‘lode’ means to lead or
to attract) and it became
"magnetic" as well.
– When freely suspended, it pointed
north-south. The magnetic compass
soon spread to Europe.
Christopher Columbus- 1492
• Used a compass
when he crossed
the Atlantic ocean
• His observations:
– the compass needle
strayed slightly
from exact north
• as indicated by the
stars
– the variation
changed during the
voyage
What’s happening?
Basically, people knew the
magnetism existed, and
learned useful applications
for it.
But, they did not understand
how it worked!
500 years ago
• William Gilbert, physician to
Queen Elizabeth I of
England, proposed an
explanation:
– “The Earth itself is a giant
magnet, with its magnetic
poles some distance away from
its geographic poles”
• Geographic poles- the points
defining the axis around which the
Earth turns
Safety with Magnets
• Magnets should not be held near
these things:
–
–
–
–
–
–
–
–
–
Credit cards
Magnetic I.D. cards
TV or VCR
Computer monitor
Floppy computer discs
Cassette Tapes/ Video Tapes
Tape Recorders
Radio
Any Speakers
– A magnet will harm most electrical
devices!!!
Using Magnetism
for Evil?!
• Magneto is a powerful
mutant with the ability to
generate and control
electromagnetic forces.
• He can shape and
manipulate magnetic fields
that exist naturally or
artificially.
• Magneto has been the XMen's most prominent
enemy ever since his first
appearance.
Magnetic Force
• Magnetism is a physical property of a substance;
the force of attraction or repulsion of magnetic
materials
– Force is stronger than gravitational force
(allows us to pick up objects using a magnet )
• Magnetic fields (half way down the page):
1. Can be mapped
2. More field lines indicates the strength of the
magnet in that area
3. Strongest near the poles
4. Stronger closer to the magnet than further
away.
Properties of Magnets
• All magnets
have two
opposite poles.
• No matter how
small or broken,
each piece will
have its own
positive and
negative pole.
S
N
S
N S
N
S
N
• There are no unpaired
poles. Poles have been labeled
as north and south.
• A magnet is capable of
producing an electric current.
• When poles get near each
other, they exert magnetic
forces on each other
– Magnetic poles that are alike
repel each other.
– Magnetic poles that are different
attract each other.
Electricity
The flow of electrons that
creates an electric current.
Magnetism
Attraction for iron associated
with electric currents
Comparing Electricity & Magnetism
Electricity
Magnetism
+ and – Charges
North and South Poles
Like Charges Repel
(-,- & +,+)
Like Poles Repel
(N,N & S,S)
Unlike Charges Attract
(+,- & -,+)
Unlike Poles Attract
(N,S & S,N)
electric field lines flow from - to +
magnetic field lines flow N to S
Double Bubble
Magnetism vs. Electricity
Magnetism
Electricity
Double Bubble
Magnetism vs. Electricity
Magnets are needed
for electricity
Opposites
Attract &
Like Repel
Magnetism
Electromagnetism
Fields
Electricity
Double Bubble
Magnetism vs. Electricity
North & South
Poles
Permanent &
Temporary
Magnets
Magnets are needed
for electricity
+ and –
Charges
Static &
Current Electricity
Opposites
Attract &
Like Repel
Magnetism
Bar, Doughnut,
& Horseshoe
Magnets
Divided further
according to
composition
Electricity
Alternating &
Direct Current
Electromagnetism
Fields
Series &
Parallel
Circuits
Double Bubble
Magnetism vs. Electricity
Opposites
Attract &
Like Repel
Electricity
Magnetism
Electromagnetism
Magnetism
• Paramagnetism - When a paramagnetic
material is placed near a magnet, it will
be attracted to the region of greater
magnetic field
– Exhibited by: materials containing transition
elements, rare earth elements and actinide
elements
• Diamagnetism - When a diamagnetic
material is placed near a magnet, it will
be repelled from the region of greater
magnetic field
– Exhibited by: all common materials, but is very weak
• Ex. People, frogs
• Ex. Metals such as bismuth, copper, gold, silver and lead, as
well as many nonmetals such as water
"Magnetic Man"
• Malaysia, Liew Thow Lin, 70
years old
• Has the ability to make metal
objects stick to his skin.
• After reading an article
about a family in Taiwan who
possessed such power, he
says he took several iron
objects and put them on his
abdomen, and to his surprise,
all the objects including an
iron, stuck on his skin and
didn't fall down.
• Pulled a car 20m along a level
surface by means of an iron
chain hooked to an iron plate
on his midriff
• Since this "gift'' is also
present in three of his sons
and two grandchildren, he
figures it's hereditary.
The boy with the magnetic
personality
•
•
•
May 11, 2011
Six-year-old Croatian, Ivan Stoiljkovic, can stick
metal objects to his body such as: spoons, mobile
phones and even frying pans
Reality: Doctors say he's ability is related to
suction properties in his skin and not to magnetic
force but anyway what he can do is very
impressive.
1.
3 Types of Magnets
Natural (Permanent) Magnet- A magnet that retains its
magnetization after removal from a magnetic field.
•
Can occur naturally.
•
Lodestone is a natural permanent magnet.
•
Can produce forces at all times
•
Earth produces a magnetic field due to molten iron in core
and spinning of the earth
•
Permanent magnets can be damaged from extreme heat and
dropping
Permanent Magnets
Each atom in a ferromagnetic
material like iron is like a little
magnet.
Lets melt the iron, and
bring in a magnetic field.
These magnets are all aligned in tiny
regions called “domains”.
At high temps these “domains” can
align in the presence of an external
field (like Earth’s) leaving a
permanent magnet.
Now, when we let the
solid cool down, and take
away the external
magnetic field, we have
formed a permanent
magnet in the same
direction as external field.
Domains
Bar Magnet
Temp
Melting
point
3 types of magnets
2. Temporary Magnet- only have
magnetic properties for a short
period of time, after exposure to
a permanent magnet
•
Iron—composed of molecules
(domains)
–
–
All different directions = no
magnetic force or pull
All lined up in one direction = force
to pull things towards them
Groups of atoms join so that their magnetic fields
are all going in the same direction
These areas of atoms are called “domains”
• An unmagnetized
• While a magnetized
substance looks like:
substance looks like:
How to demagnetize a magnet:
1. Impact (hit it)
2. Heat it
3. Electricity
This causes the domains
to become random again!
3 types of Magnets
3. Electromagnet- temporary magnet, made by
coiling wire around a piece of soft iron.
– When an electric current is passed through the wire, a
magnetic field is produced.
– The field magnetizes the iron core by aligning domains
within the iron.
1. What happens if a magnet breaks in
half?
–
–
–
–
One half has a north pole only, and one half
has a south pole only
Neither half will have a pole
Each half will be a new magnet, with both a
north and south pole
Neither half will attract or repel.
2. Draw arrows to show if the cars attract
or repel each other. On the space to the
right, write the word that describes the
action of the cars (attract or repel).
3. The region around a magnet where the
magnetic force is exerted is known as
its
–
–
–
magnetic pole
magnetic field
magnetic domain
4. Magnetism can be considered a
–
–
–
nuclear property
physical property
chemical property
5. A temporary magnet
–
–
–
keeps its magnetism for a long time
cannot be destroyed
easily loses its magnetism
S
N
• Attract 
• Attract 
• Repel 
S N
S N
What on Earth is a Cow Magnet?
• Magnets come in many shapes
and sizes, but the cow magnet
was invented to solve a very
serious problem of dairy
farmers.
• When the cow grazes, it often
consumes and swallows small
pieces of iron: baling and barbed
wire, staples, nails, and other
metallic objects.
• These objects are indigestible
and lodge in the reticulum and
cause inflammation.
• This results in lower milk
production (for dairy cattle) or
lower weight gain (for feeder
stock).
• This condition is called hardware
disease.
• Solution: A rancher/ farmer
feeds a magnet to each calf
at branding time; the magnet
settles in the rumen or
reticulum and remains there
for the life of the animal.
• The cow magnet attracts
such objects and prevents
them from becoming lodged in
the animal's tissue. While the
resultant mass of iron
remains in the cow's rumen as
a sort of bezoar, it does not
cause the severe problems of
hardware disease.
• One small cow magnet can
help a cow for her whole life!
Magnetic Fields
Procedure:
1. Place a magnet into a tray, put a piece of paper
over the magnet.
2. Lightly sprinkle iron filings on and around the
magnet, gently tap the paper.
3. Observe the formation around the magnets,
and sketch what you see.
Types of Demonstration:
1. One magnet
2. Two magnets- Attracting
3. Two magnets- Repelling
Mapping Magnetic Fields
• One Magnet
N
S
• Two Magnets- Attracting
N
S
N
S
S
N
• Two Magnets- Repelling
N
S
MAGNETIC FIELDS- One
Magnet
• This picture demonstrates what occurs when
one magnet is placed on paper, and iron
filings are sprinkled around it.
MAGNETIC FIELDS- Two
Magnets Attracting
• This picture has two magnets placed on a
piece of paper with their opposite poles
facing each other, and iron filings are
sprinkled around them.
MAGNETIC FIELDS- Two
Magnets Repelling
• Pictured here are two magnets placed on a
piece of paper with their like poles facing
each other, and iron filings are sprinkled
around them.
Like poles repel…
Opposite poles attract!
The Earth’s magnetic field extends far into
space. It is called the “magnetosphere.”
When the magnetic particles from the sun, called “solar
wind”, strike this magnetosphere, we see a phenomenon
called…
The Aurora Borealis in the Northern HemisphereAnd the
Aurora Australis in the Southern Hemisphere
1. True / False. You can see
1. False. Magnetic fields are
magnetic fields without
invisible (until you use iron
assistance.
filings to help map them!).
2. By looking at magnetic field
patterns, you can tell where the
2. Magnetic force is strongest
magnetic forces are the
strongest. Where are you
at the poles.
looking and what do you see?
– Where all of the lines
3. You can tell by these lines
converge/intersect
whether the magnets are
(A)
– Where the lines are most
attracting, or (B) repelling.
What would each look like??—
concentrated
sketch and describe.
3.(A) Attracting- lots of
lines connecting between
them
(B) Repelling- lines do not
interact or touch—nothing
observed between the
magnets
Electricity/Magnetism Videos
Electricity Notes
A. Intro
• All matter is composed of atoms.
• Atoms are made up of smaller particles
called protons, neutrons, and electrons.
• Protons are positively charged and
electrons are negatively charged.
• According to the law of electric
charges, like charges repel and opposite
charges attract.
• If an atom loses electrons it becomes
positively charged. If an atom gains
electrons it becomes negatively
charged.
There are three ways to “charge” an object...
1. Conduction– e- are transferred by direct contact
Ex) uncharged metal & + charged glass rod
(e- travel from metal to glass rod leaving the metal +
charged)
2. Induction- when charges in an uncharged object
are rearranged w/o direct contact
Ex) – charged balloon and neutral wall
(+ charged object near a neutral object and e- in
neutral object are attracted to + charged object
& move towards it)
3. Friction- when two objects are rubbed together
electrons are “wiped” from one to another
Ex) rub a plastic ruler with a cloth
(e- are transferred from the cloth to the ruler)
Charge can be detected by using an Electroscope.
Ex) Glass flask with a metal rod inserted through a rubber stopper.
There are two metals leaves at the bottom of the rod.
Leaves hang straight down when not charged and move apart when charged.
Uncharged
Charged
Static Electricity
• Static – not moving
• Static electricity is the build up of charges
on an object.
• The charges that create static electricity do
not move away from the object they are
stuck to.
Why do clothes stick together after they
are taken out of the dryer?
When you dry clothes in the dryer,
different fabrics rub together, and
electrons from a cotton sock (for
instance) may rub off onto a polyester
shirt. That's why clothes sometimes
stick together and make sparks when
you pull them apart.
How does a fabric softener (dryer sheet)
work to prevent static cling?
As these sheets bounce around with
your clothes, they add a uniform
antistatic coating to the fabric. Rather
than cotton rubbing against polyester,
you've got the antistatic coating on the
cotton rubbing against the antistatic
coating on the polyester. No electrons
rub off and you don't get any static
cling.
• The loss of static electricity is discharge.
• Gradually, over time, charges that build up on
an object leave the object.
• Electric discharge may happen rapidly or
slowly.
• The most dramatic example of electric
discharge is lightning.
Current Electricity
• Electric current is a continuous flow of
electrons.
• Current is how fast charge passes at a given
point.
• There are 2 types of electric current:
Alternating Current (AC) and Direct Current
(DC).
• Electric current produced by batteries is
DC and electric current from your home
outlet is AC.
• Current in a wire is determined by voltage
and resistance. The higher the voltage, the
more energy is released.
• Resistance is the opposition to the flow of
electric charge.
• It is represented with the symbol Ω .
• The higher the resistance, the less current
is in it.
• Resistance can change depending on an
object’s material, thickness, length, and
temperature.
• An example of a material that has a low
resistance is copper.
• Iron is a good conductor.
• Materials with a low resistance are used to
make wires.
• A thick pipe has less resistance because
there are more spaces for current to travel
through.
• A thin pipe has more resistance because it
does not have to move around many spaces.
• In general, resistance increases as the
temperature of a metal increases.
• This happens because atoms move faster at
higher temperatures and get in the way of
electric charge.
• If you cool certain materials, resistance will
drop to zero.
• These materials are known as
superconductors.
• They can be useful because very little energy
is wasted when current travels through
them.
Where to find the Vocabulary Words:
Word
Sciencesaurus
Insulator
p. 317
Conductor
p. 317 & 477
Static Electricity
p. 316 & 516
Current Electricity
p. 317 & 479
Alternating Current
p. 317 & 468
Direct Current
p. 317 & 481
Circuit
p. 318 & 475
Circuit Symbols
* Glue or Tape * to each
corresponding index card
Open Circuit
p. 318
Closed Circuit
p. 318
Series Circuit
p. 319 & 514
Parallel Circuit
p. 319 & 505
Circuit Diagram
Open Circuit
The absence of flow of electrons
through a circuit because of an
opening in the circuit.
Ex) Lights Off
Closed Circuit
An electric current providing an
uninterrupted, endless path for
the flow of electrons.
Ex) Lights On
Series Circuit
A circuit having one path for the
electricity to flow.
If one bulb goes out, the circuit is open
and they all go out!
Ex) old x-mas tree lights & fuses
Parallel Circuit
A circuit having MORE than one path for
the electricity to flow – “branches”.
If one bulb goes out, the rest can stay on
w/ their own path!
Ex) Most things in your household…
lights, appliances, etc.
Back – Measuring Electricity
Word
Current
Voltage
Resistance
Capacitor
Definition
Units
Water
Analogy
Pic/Symbol
Word
Current
Voltage
Resistance
Capacitor
Definition
Units
Water Analogy
H20 Flow –
Current
Water
Pressure- Amt
of flow
Difficulty of
water flow due
to Pipe Size or
Dam
Water storage
– Reservoir
- Dam
Pic/Symbol
Word
Definition
Resistance
Capacitor
Water Analogy
Flow of e-
H20 Flow –
Current
Electrical
Pressure
Water
Pressure- Amt
of flow
Limits the
amount of
e- current
Difficulty of
water flow due
to Pipe Size or
Dam
Stores
Electricity
Water storage
– Reservoir
- Dam
Current
Voltage
Units
Pic/Symbol
Word
Definition
Units
Flow of eCurrent
Voltage
Resistance
Capacitor
Amps
(Amperes)
Electrical
Pressure
Limits the
amount of
e- current
Stores
Electricity
Volts
Ohms
Farads
Water Analogy
H20 Flow –
Current
Water
Pressure- Amt
of flow
Difficulty of
water flow due
to Pipe Size or
Dam
Water storage
– Reservoir
- Dams
Pic/Symbol
Back – Measuring Electricity
Word
Definition
Units
Water
Analogy
Current
Flow of e-
Amps
(Amperes)
H20 Flow –
Current
Voltage
Electrical
Pressure
Resistance
Capacitor
Limits the
amount of
e- current
Stores
Electricity
Volts
Ohms
Farads
Water
PressureAmt of flow
Difficulty of
water flow
due to Pipe
Size or Dam
Water
storage
-Reservoir
- Dam
Pic/Symbol
3 Things Needed to Create
Electricity
1. Magnet
2. Conductor
3. Motion
Amp
Measures
Electrical Current
[The Volume of the Current]
SI Unit = Ampere.
Volt (V)
Measures
Electrical Pressure
{The Force or Push of
Electricity}
SI Unit = Volts
Ohm
Ω
Measures Electrical Resistance
{How difficult it is for the
current to pass through}
SI Unit = Ohm
Resistance
Measures how difficult it is
for electricity to pass
through an object.
SI unit = Ohm
Ω
Electrical Resistance
Low Resistance
• Easy to get through
• Good Conductors (copper, gold, etc)
• Large/Thick Wires
High Resistance
• Tough to get through
• Good Insulators (glass, rubber, etc)
• Small/Thin Wires
Plumbing Pipe Analogy
• Voltage/Volts (V) = Water Pressure
– It determines how fast the electrons
will travel through the circuit.
• Current/Amps = Flow Rate
– A measure of the volume of
electricity that flows past a given
point.
• Resistance/Ohms = Pipe Size
– Measures the difficulty of electric
flow
Electrifying Electrifoldable Quiz!
• Part I = 20 Matching
– 5 points each
– 100 points
• Part II = Thinking Maps
– 10 parts x 10 points each
– 100 points
Part I: Matching
1. ___ A material that does not allow
electricity to pass through it easily
2. ___ A circuit with more than one path for
electricity to flow
3. ___ Lightning is an example of this type of
electricity
4. ___ A type of circuit where if one bulb
goes out they all go out
5. ___ Copper, zinc, and gold are examples
6. ___ A type of current electricity that
flows in 1 direction
7. ___The flow of electrons that creates an
electric current
8. ___ Negative charges attract…
9. ___ Measures electric current
10. ___A type of circuit where electrons are
able to flow because there are no openings
11. ___ Negative charges repel…
12. ___ Measures electrical pressure
13. ___ Load
14. ___ Light, wires, and a battery
15. ___ Has both north and south poles
16. ___ 2 types of Current Electricity
17. ___ Motion, conductor, and a magnet
18. ___ A circuit with an opening
19. ___ Stores electricity
20. ___ Unit used to measure resistance
Answers
1. S - Insulator
2. K – Parallel Circuit
3. D – Static Electricity
4. C – Series Circuit
5. B - Conductors
6. F – Direct Current
7. G - Electricity
8. H – Positive Charges
9. T - Amps
10. I – Closed Circuit
11. J – Negative Charges
12. O - Voltage
13. L - Light
14. M – 3 parts of a Circuit
15. E - Magnet
16. N – AC/DC
17. P – 3 things for
Electricity
18. Q – Incomplete Circuit
19. R - Capacitor
20. A - Ohm